BCP

A BCP is an RFC -- an Internet/IETF Request for Comments document; the standards for the Internet -- which has been tagged as promulgating Best Current Practices.

Best Current Practices are the Internet's best idea of the ways in which it itself should be built and operated, the approaches which will make it work the best and fastest, and be the hardest for bad actors to attack.

RFC numbers change, if a document is reissued in a new version (there are no 'version numbers or release dates' for RFCs); this is not true of BCP numbers: if RFC2827 were reissued as RFC, say, 9000, that would then become BCP38.