RFC

RFC is short for Request For Comment. The entire internet is basically specified as a series of numbered RFCs.

Not all RFCs are standards. Each RFC is assigned a status category. This status is one of the following: Informational, Experimental, Best Current Practice, Standards Track, or Historic.

RFCs do not change. If a newer version becomes available, it is assigned a new RFC number.

RFCs are available for download free of charge. "Home" of the RFCs is the IETF web site: https://www.ietf.org/standards/rfcs/