Newcomers to codegolf.SE are often compelled to ask what many of our abbreviations and terms mean. Let us list them here so this information always will be easily available.
Abbreviations marked with a star (*) are chat specific.
Catalog: A type of simple on-topic challenge where the challenge's aim not so much to find a winner as it is to create a catalog of solutions in many languages.
CG: Code Golf; a challenge to solve a particular problem with the shortest code.
CGCC: Code Golf & Coding Challenges; our official abbreviation for the main Stack Exchange site for coding competitions.
*CMC: Chat Mega Challenge; usually a challenge posted jokingly in chat due to it being very involved or outright impossible. Example.
*CMP: Chat Mini Poll; a request for opinions on a stated question, often about programming language design. Example.
*CMQ: Chat Mini Question; usually an alternative to a CMM, but more general (not necessarily restricted to Meta-like questions)
CnR: Cops and Robbers; challenges where one person has to "crack" another person's code.
CR: Code Review; jokingly our archenemy in the sense that they value efficient legible code while we value obscure inefficient code.
Eleven: To delete something using moderator powers, e.g. "Yeah, the post is gone, Dennis 11'd it". mod abuse -> mod abuse!!! -> mod abuse !!11!1!! -> mod abuse !!eleven!1!! -> mod abuse eleven -> eleven
Hammer: To close a challenge single-handedly; users that have a gold tag badge in one of the posts's tags have the privilege to close it as a duplicate by themselves; moderators can also single-handedly close any question.
FGITW: Fastest Gun in the West; a quick submission to a just-posted challenge, typically used in reference to the problem that fast answers get more visibility and upvotes than later but better ones.
HNQ: Hot Network Questions; a global page where popular Stack Exchange posts are often featured. Also the corresponding global sidebar.
KC: Kolmogorov Complexity; a challenge to compress a static output.
KotH: King Of The Hill; a game where the submissions interact with and compete against each other in some form of game.
LQA: Low Quality Auto; these are reviews that show up in the review queue from being short or containing only code.
*NSP or *NSQ: New Sandboxed Posts/Questions; a chat bot which posts in TNB whenever a new challenge is proposed in the Sandbox.
OEIS: The On-Line Encyclopedia of Integer Sequences; as the name says a website that collects all kinds of integer sequences and assigns them a name, e.g. the squares are A000290. Frequently cited in sequence challenges.
PopCon: Popularity Contest; a competition where the answer with the highest vote tally (upvotes minus downvotes) wins.
PPCG: Programming Puzzles & Code Golf; the old name for this site.
Proper quine: A program that not only prints itself (see quine) but also obeys the proper quine rules.
Quine: A program that prints its own source code. See also proper quine.
Spec: Short for the specification of a challenge.
*TNB: The Nineteenth Byte; our principal chatroom.
*TNBDE: TNB Data Explorer.
VTC: Vote To Close; usually called a CV (Close Vote) on the rest of Stack Exchange.
VTR: Vote To Reopen.
VTD: Vote To Delete.