FYI is a common abbreviation of For Your Information. On the Internet, FYIs are a subset of the RFC series. The following description is taken from FYI 1, the FYI on FYIs:
The FYI series of notes is designed to provide Internet users with a central repository of information about any topics which relate to the Internet. FYIs topics may range from historical memos on "Why it was done this way" to answers to commonly asked operational questions.
