The full title is the Combined Community Codec Pack. Actually, it's more a filter pack than a codec pack, but filter doesn't begin with C and we wanted a good acronym. The name is also a pun on the Russian name for USSR, Союз Советских Социалистических Республик, abbreviated as "СССР". Should you be appalled by this choice of name, Blame movax.
Jokes aside, the CCCP was created to replace the video playback packs provided by several anime fansub groups in favor of a single reliable pack capable of decoding practically any groups' files - without breaking compatibility for other formats. Since then it has grown into a pack that can decode more or less anything that you will run into during your travels on the internet.
Product page: here