Apparently it stands for “Create A Pokemon”. What is it, and are questions about it allowed on PokéBase? Is it part of Showdown! and smogon?
It's a format made by Smogon and playable on Showdown!.
Composition Create-a-Pokémon (commonly referred to as the CAP Metagame or simply CAP) is a format based on OU which features all Pokémon created by the Create-A-Pokémon Project. The addition of 22 unique Pokémon makes this format quite different from standard OU, though many of OU's top threats still thrive in this format. To learn more about the CAP Project, check out this guide for newcomers and visit the CAP Project forum. The CAP Metagame has its own subforum where you can discuss the format. CAP has a room on Pokémon Showdown! as well as an IRC channel where you can discuss anything related to CAP.
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