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I've often seen "bis" appended to versions of protocols (eg v.34bis or httpbis).

What does "bis" mean or stand for?

A telecom engineer I know thinks it might be French in origin.

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    Is the question about the general meaning of "bis" or more specific to how HTTPbis relates to HTTP?
    – Bruno
    Commented Feb 2, 2012 at 0:54
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    @Bruno - it was specifically about what bis means in general, but I'd definitely be interested in http vs httpbis
    – J. Polfer
    Commented Feb 2, 2012 at 0:56
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    I encourage the IETF to be a bit more courteous. Those who read these specifications already know to expect detailed and dry documents, so presenting them right off the bat with an obscure term "bis" is not helpful. :-) A search on IETF shows no explanation of "bis" so they would do well to at least provide a note about "bis" meaning e.g. in the "About" page. I sent IETF an email about it.
    – user2534096
    Commented Aug 30, 2021 at 22:35

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As others have already said, "bis" comes from "twice" or "repeat". It's used to indicate a second variant of something (although usually with only minor variations that don't warrant a new name).

In the context of HTTP, HTTPbis is the name of the working group in charge of refining HTTP. According to its charter:

HTTP is one of the most successful and widely-used protocols on the Internet today. However, its specification has several editorial issues. Additionally, after years of implementation and extension, several ambiguities have become evident, impairing interoperability and the ability to easily implement and use HTTP.

The working group will refine RFC2616 to:

  • Incorporate errata and updates (e.g., references, IANA registries, ABNF)
  • Fix editorial problems which have led to misunderstandings of the specification
  • Clarify conformance requirements
  • Remove known ambiguities where they affect interoperability
  • Clarify existing methods of extensibility
  • Remove or deprecate those features that are not widely implemented and also unduly affect interoperability
  • Where necessary, add implementation advice
  • Document the security properties of HTTP and its associated mechanisms (e.g., Basic and Digest authentication, cookies, TLS) for common applications

It will also incorporate the generic authentication framework from RFC 2617, without obsoleting or updating that specification's definition of the Basic and Digest schemes.

Finally, it will incorporate relevant portions of RFC 2817 (in particular, the CONNECT method and advice on the use of Upgrade), so that that specification can be moved to Historic status.

In doing so, it should consider:

  • Implementer experience
  • Demonstrated use of HTTP
  • Impact on existing implementations and deployments

The Working Group must not introduce a new version of HTTP and should not add new functionality to HTTP. The WG is not tasked with producing new methods, headers, or extension mechanisms, but may introduce new protocol elements if necessary as part of revising existing functionality which has proven to be problematic.

The last paragraph (emphasis mine) explains why they've used "bis" in this context, since they explicitly don't want a new version.

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bis

The word (also used as a prefix or suffix) bis , applied to some modem protocol standards, is Old Latin for "repeat" (akin to Old High German "twice"). When a protocol ends with "bis," it means that it's the second version of that protocol.

Similarly, ter is from Old Latin meaning "three times." The suffix terbo in the V.xx modem protocol is an invented word based on the Old Latin ter and the word turbo (Latin for "whirling top" or "whirlwind") meaning "speed." V.32terbo is the third version developed of the V.32 modem protocol..

(from http://whatis.techtarget.com/definition/0,,sid9_gci211669,00.html)

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