I have seen the two words being used over and over again here but don't know whether they are synonyms of each other or not. The Usage guides for the two tags seem incomplete and confusing.
Can somebody elaborate about the 'transit' part?
Layover AFAIU it, is you are in the airport for some hours between connections (very similar to trains) but that's about it.
"Layover" means to await a connecting flight at an airport.
For instance, you may fly from New Delhi to Chennai with a three hour layover in Mumbai.
"Transit" means to pass through (physically enter and then exit) a country on the way to another country, usually without having any other purpose for being in that country. In air travel, this happens during a layover.
For instance, you may transit the United Kingdom on your layover at Heathrow Airport, waiting for your connecting flight to New York.
No, they don't:
Passing through a place briefly while travelling on the way to somewhere else.
The period of time spent waiting for a connection (unlike stopover this is not chosen by the traveller).
For example, for transit there is no mention of "connection", and for layovers there is no mention of "briefly".
They are both related to travel, that is the nature of this site, and they both involve a hiatus so in some circumstances either would be equally applicable. Also, being of similar meaning they will at times be misused.
A layover is generally static (eg spent sat in an airport terminal). Transit generally involves motion, thus @phoog's example, as:
in the case of someone who wants to drive from Canada to Mexico.
Given we also have stop-overs:
Scheduled stop in the middle of a transit decided by the traveler.
and it is generally the traveller that chooses their route (from those available) the selection of 'layover' rather than 'stopover' may suggest a measure of inconvenience (say from the delay). Similarly, 'transit' tends to incorporate the interval into the journey as a whole, and since presumably that is willingly undertaken, is quite welcomed. Whereas 'layover', by emphasising the break in the journey, is not welcomed.
No they don't.
"Transit" is immigration jargon. It refers to travel through a country (or a block of countries with common border control) for the purpose of getting to another country.
In most countries "transit" may be further divided into "airside transit" where a passenger remains in a secured area and does not pass through immigration checks and "landside transit" where a passenger does go through immigration checks.
"layover" is airline jargon. It means stopping at an airport for the purpose of changing from one flight to another on the same ticket. Usually there are time limits on layovers to distinguish them from stopovers.
Often the two come together but not always. If someone drives from manchester to moscow they have transited a number of countries but not had a single layover. If they fly from manchester to london to paris they have had a layover in london but they did not enter a country in transit.
