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From time to time, I come across some unusual mathematical terms. I know something about strange attractors. I also know what Witch of Agnesi is. However, what prompted me to write this question is that I was really perplexed when I read the other day about monstrous moonshine, and this is so far my favorite, out of similar terms.

Some others:

Are there more such unusual terms in mathematics?

Jan 17 update: for fun, word cloud of all terms mentioned here so far:

enter image description here

and another, more readable:

enter image description here

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    $\begingroup$ I've always been tickled by 'Fuzzy Logic.' $\endgroup$
    – Peter Woolfitt
    Commented Jan 13, 2015 at 17:30
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    $\begingroup$ The `Golden ratio' $\phi$. $\endgroup$
    – pshmath0
    Commented Jan 13, 2015 at 17:37
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    $\begingroup$ It may say more about me than about math, but if I need to give a strange sounding math term, then perverse sheaves is my go-to-answer. $\endgroup$
    – Jyrki Lahtonen
    Commented Jan 13, 2015 at 17:48
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    $\begingroup$ Shouldn't this be CW? $\endgroup$
    – Asaf Karagila ♦
    Commented Jan 13, 2015 at 18:22
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    $\begingroup$ “The question is widely applicable to a large audience. A detailed canonical answer is required to address all the concerns.” what. $\endgroup$
    – k.stm
    Commented Jan 15, 2015 at 19:21

39 Answers 39

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I've always liked 'abstract nonsense'.

To quote wikipedia:

Note that referring to an argument as "abstract nonsense" is not supposed to be a derogatory expression, and is actually often a compliment regarding the generality and sophistication of the argument.

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    $\begingroup$ and don't forget "highly abstract nonsense" $\endgroup$
    – Alan
    Commented Jan 13, 2015 at 19:20
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    $\begingroup$ General abstract nonsense. $\endgroup$
    – k.stm
    Commented Jan 14, 2015 at 21:06
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    $\begingroup$ Special abstract nonsense! $\endgroup$
    – Bob Jarvis - Слава Україні
    Commented Jan 15, 2015 at 18:45
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    $\begingroup$ I thought it was "generalized abstract nonsense". $\endgroup$
    – aaazalea
    Commented Jan 15, 2015 at 19:03
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Complex theorems often use simple, illustrative names.
Ham Sandwich Theorem
No Free Lunch Theorem
Ugly Duckling Theorem

Some are named by the scenario they are describing
Birthday Attack
Doomsday Argument

Other by the accompanying real-life events
Happy Ending Problem

and finally the top 10 Dirty Mathematics from Spikedmath (slightly edited to take up less space) enter image description here
A Survey on Cox Rings
Cox-Zucker machine

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    $\begingroup$ Good examples. However, /ˈlɑːtɛx/ is not (should not be) pronounced Lay-tech, that's just typical americanisation of syllables. The fault is with the original poster of the image but it bothers me :) $\endgroup$
    – orion
    Commented Jan 15, 2015 at 10:14
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    $\begingroup$ You have the IPA above ("Lah-tech" is you want, where "tech" rhymes with Scottish "loch"). That's how the entire world says it (pronouncing "a" as "eye" is english-only thing), and that's how it was originally intended. However, due to constant ignorance and abuse, the alternative used above is usually stated as acceptable. The last syllable is also constantly pronounced wrongly, but that's another matter. $\endgroup$
    – orion
    Commented Jan 16, 2015 at 8:03
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    $\begingroup$ @DenDenDo I believe that the X in $\LaTeX$ is actually supposed to be a chi, but I'm not 100% sure. $\endgroup$
    – apnorton
    Commented Jan 18, 2015 at 5:02
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    $\begingroup$ Call me naive, but why is #7 dirty?! $\endgroup$
    – rschwieb
    Commented Jan 19, 2015 at 11:31
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    $\begingroup$ I know this is comment thread necromancy, but... @orion: Per Lamport, /ˈleɪtɛx/ is perfectly acceptable, as is /ˈlɑːtɛx/. "One of the hardest things about LaTeX is deciding how to pronounce it.This is also one of the few things I'm not going to tell you about LaTeX, since pronunciation is best determined by usage, not fiat. TeX is usually pronounced teck, making lah-teck, and lay-teck the logical choices; but language is not always logical, so lay-tecks is also possible." Not simply a crude Americanism, despite your insinuations. :-) $\endgroup$
    – Brian Tung
    Commented Sep 27, 2019 at 16:18
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Hairy Ball Theorem

No Hair Theorem

Arnold's Cat Map (this kills the cat)

No Ghost Theorem

The condom/glove problem (do NOT do this)

Buridan's Ass Paradox

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    $\begingroup$ Is Buridan's Ass mathematical? I've heard of it, but never in the context of mathematics. $\endgroup$
    – KSmarts
    Commented Jan 13, 2015 at 20:10
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    $\begingroup$ Yes, see this paper by Leslie Lamport: research.microsoft.com/en-us/um/people/lamport/pubs/buridan.pdf $\endgroup$
    – Alex R.
    Commented Jan 13, 2015 at 22:05
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    $\begingroup$ Whoever came up with the solution to the condom problem has apparently never used a condom. $\endgroup$
    – tmastny
    Commented Jan 14, 2015 at 1:08
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    $\begingroup$ When I once told someone of the hairy ball theorem he found it funny that it was discovered by someone named “Harry Ball”. $\endgroup$
    – k.stm
    Commented Jan 15, 2015 at 8:09
  • $\begingroup$ no kill cat plz thankyou $\endgroup$
    – bjb568
    Commented Jan 16, 2015 at 3:25
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I've always been fond the term pointless topology.

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While the pronunciation is French, there is the Tits Group.

There's also the Dragon family of fractal curves. Also, related to Cantor dust is the Menger sponge. Actually, fractals give a lot of fun ones, such as Douady rabbit (and related "fat rabbit"), Mandelbulb, Pythagoras Tree, the Flowsnake, and the Minkowski Sausage.

In recreational mathematics, with some applications to number theory, numbers can be happy or sad/unhappy; evil or odious; economical, equidigital, or wasteful; or lucky. Edit: They can also be solitary or friendly, which made me think of XKCD.

Computability theory has Busy Beavers.

So, "Are there more such unusual terms in mathematics?" Yes.

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  • $\begingroup$ As a colleague of mine likes to point out, changing the pronunciation from 'tits' to 'teats' just substitutes a different name for the same thing(s), so it's not clear that it makes it less risqué. $\endgroup$
    – LSpice
    Commented Dec 11, 2018 at 22:08
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I always wanted to get a room at the Hilbert Hotel.

I also love working with annihilators....

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    $\begingroup$ All of our rooms are occupied... How long will you be staying? $\endgroup$
    – KSmarts
    Commented Jan 13, 2015 at 20:07
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    $\begingroup$ That's a shame because I have an infinite amount of millionaire friends who wanted to dine at the restaurant.... $\endgroup$
    – Eleven-Eleven
    Commented Jan 13, 2015 at 20:12
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    $\begingroup$ @Eleven-Eleven Countable or uncountable? Are they drinking beer? Do they know their limits? $\endgroup$
    – flawr
    Commented Jan 13, 2015 at 21:32
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    $\begingroup$ @flawr, well, countable of course. Actually, the first mathematician will order a pint of beer, the second will order a half a pint, the third will order a quarter of a pint...so if the bartender is smart,.... $\endgroup$
    – Eleven-Eleven
    Commented Jan 14, 2015 at 13:49
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A Killing field is not as bloody as it sounds; it's actually a certain type of vector field named after Wilhelm Killing.

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The function $$f(x)=\left\{\begin{array}{rcl}\frac{1}{q}&:&x\in\mathbb{Q}\text{ and }x=\frac{p}{q}\text{ in lowest terms}\\0&:&x\notin \mathbb{Q}\end{array}\right.$$ is called (among other things) the Stars over Babylon.

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  • $\begingroup$ The popcorn / Christmas-tree function! $\endgroup$
    – LSpice
    Commented Jan 18, 2015 at 16:20
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While categories are often called "Cats", in set theory we have mice and weasels.

(We also have morasses, which sound pretty weird, but one look at the definition and you see that the name is very accurate in describing the object.)

I recently sat in a lecture where someone defined a "piste" (ski slope).

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    $\begingroup$ And premice! (Or is there another phrase for those now?) $\endgroup$
    – Steven Stadnicki
    Commented Jan 13, 2015 at 21:28
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The Chicken McNugget Theorem.

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  • $\begingroup$ Hilarious name indeed! Could not resist myself from sharing it in my Facebook. $\endgroup$
    – aghost
    Commented Jan 14, 2015 at 21:50
  • $\begingroup$ Numberphile did a video on this, IIRC. $\endgroup$
    – Akiva Weinberger
    Commented Jan 14, 2015 at 23:33
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Here's my favorite: cleavage (SFW).

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    $\begingroup$ The URL contains "show/cleavage". That in and of it self felt like a risky click. Alas, disappointed at the safety of it. $\endgroup$
    – Axoren
    Commented Jan 14, 2015 at 11:44
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    $\begingroup$ @Axoren How is “cleavage” ever a risky click? $\endgroup$
    – k.stm
    Commented Jan 14, 2015 at 21:09
  • $\begingroup$ When you're at work. $\endgroup$
    – Axoren
    Commented Jan 14, 2015 at 22:25
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    $\begingroup$ @Axoren Added a SFW tag. $\endgroup$
    – Brian Fitzpatrick
    Commented Jan 14, 2015 at 22:52
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The monster group
A group with $808017424794512875886459904961710757005754368000000000$ elements.

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    $\begingroup$ An article about them in Scientific American was titled "The capture of the monster". $\endgroup$
    – VividD
    Commented Jan 13, 2015 at 18:12
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    $\begingroup$ Do not forget the Baby Monster Group. $\endgroup$
    – flawr
    Commented Jan 14, 2015 at 8:58
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The Hairy Ball theorem and forgetful functors make me giggle!

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    $\begingroup$ What did the forgetful functor do for her stoner friend? She left a joint as a free object! $\endgroup$
    – Yuri Sulyma
    Commented Jan 14, 2015 at 3:00
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Diagram chasing is rather fun.

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The concept of a Syzygy always tickled me, as do Zero-Knowledge Proofs. Of course I'd be remiss were I not to mention Gropes.

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Alien Ring Structure - from Mochizuki's papers on inter-universal Teichmuller theory.

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  • $\begingroup$ That stuff looks Alien to me. $\endgroup$
    – Ali Caglayan
    Commented Jan 14, 2015 at 0:13
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Would you like to zigzag inside the random forest of some beautiful tropical geometry? But keep an eye on voracious ant colonies!

Tropical cubic curve

(The image shows a tropical cubic curve, stolen from Wikipedia.)

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Exotic spheres (differentiable manifolds which are homeomorphic but not diffeomorphic to an $n$-sphere).

The Alexander horned sphere (this shows the Jordan–Schönflies theorem doesn't hold in $3$ dimensions).

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Devil's staircase

Blancmange function

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Not exactly math, but physics is close enough. There are higher derivative of velocity called jerk, jounce, snap, crackle and pop.

And there's also screw theory.

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Some examples could be:

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Although the term may not really be in common use: A paper about "Generalized staircases: Recurrence and symmetry" refers to a figure showing a certain surface at page 10, and calls it

"The eierlegende Wollmilchsau surface"

The term eierlegende Wollmilchsau literally means "egg-laying wool-milk-sow", and refers to any (usually imaginary) thing that "can do everything" or "has many positive properties". In this case, the surface has many properties that usually are not found in this combination in other surfaces.

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The famous "pons asinorum" (Euclid's Elements, Book I, prop. 5), which literally means "bridge of asses (donkeys)" in Latin.

Pascal's limaçon curve (French for snail).

Another mathematical term that I find peculiar is "totient" (as in the Euler $\phi$-function. Apparently, it was first introduced by J. J. Sylvester.

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    $\begingroup$ Couldn't you also translate that as "bridge of asses"? Or "ass-bridge"? That's much more fun. $\endgroup$
    – KSmarts
    Commented Jan 13, 2015 at 20:10
  • $\begingroup$ Sure, an ass is a donkey after all. :-) $\endgroup$
    – Kim Fierens
    Commented Jan 13, 2015 at 20:20
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    $\begingroup$ Sylvester invented all kinds of strange mathematical words: syzygy (mentioned above), catalecticant, cumulant, cyclotomic, etc. $\endgroup$
    – user64687
    Commented Jan 14, 2015 at 16:25
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There are topological spaces called hedgehog spaces. According to the linked Wikipedia article, a $K$-hedgehog space is sometimes said to have "spininess $K$."

And let's not forget the process of blowing up points on a plane.

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Graph Theory has its "snarks".

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    $\begingroup$ What about grumpkins? $\endgroup$
    – Asaf Karagila ♦
    Commented Jan 13, 2015 at 22:38
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Be sure to check out wikipedia's List of humorous units of measurement, with such gems as:

Helen of Troy (from the Iliad) is widely known as "the face that launched a thousand ships". Thus, 1 millihelen is the amount of beauty needed to launch a single ship.

A Kardashian is a unit of measure representing 72 days of marriage.

The beard-second is a unit of length inspired by the light-year, but used for extremely short distances such as those in integrated circuits. The beard-second is defined as the length an average beard grows in one second.

The Wheaton is a measurement of Twitter followers relative to celebrity Wil Wheaton. The measurement was standardized when Wil Wheaton achieved half a million Twitter followers, with the effect that Wil Wheaton now has 5.52 Wheatons himself (as of January 2015). As few Twitter users have millions of followers, the milliwheaton (500 followers) is more commonly used.

And also wikipedia's List of unusual units of measurement.

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    $\begingroup$ This isn't exactly mathematical, as units are characteristic to the natural sciences (i.e., physics) and math can/does do live without. $\endgroup$
    – Nox
    Commented Jan 15, 2015 at 22:39
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    $\begingroup$ It's not exactly non-mathematical, either, as units are quite relevant to mathematics. $\endgroup$
    – Ehryk
    Commented Jan 15, 2015 at 22:58
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For the botanists here: I'd like to add Euclid's orchard and the opaque forest problem which is rather from the field of computer graphics, but still got some maths in it.

EDIT: And of course the Sexy Primes as well as wild and tame knots.

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The Wiener Sausage is what the nbhd's of a Brownian motion trace out.

One might argue things named after Norbert Wiener or Mark Kac are not unusual since they were relatively famous mathematicians. But its still funny.

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  • $\begingroup$ Sorry to be a party-pooper (ahem), but "Kac" is pronounced like "Katz". $\endgroup$
    – user64687
    Commented Jan 16, 2015 at 10:33
  • $\begingroup$ Supposed to be pronounced like Katz. Doesn't mean people pronounce it that way in reality. =) $\endgroup$
    – Batman
    Commented Jan 16, 2015 at 16:39
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Here is one from sorting.

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I've always been fond of the spectral theorem.

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