Page "Request for Comments" Paragraph 40

The best current practice ( BCP ) subseries collects administrative documents and other texts which are considered as official rules and not only informational, but which do not affect over the wire data.

The border between standards track and BCP is often unclear.

If a document only affects the Internet Standards Process, like BCP 9, or IETF administration, it is clearly a BCP.

If it only defines rules and regulations for Internet Assigned Numbers Authority ( IANA ) registries it is less clear ; most of these documents are BCPs, but some are on the standards track.