FPN: See 90.7, Examination of Equipment for Safety, and
110.3, Examination, Identification, Installation, and Use of
Equipment. See definitions of Approved, Identified, Labeled,
and Listed.

FPN is an acronym for "Fine Print Note"

FPNs are not part of the offcial language of the NEC and are not to be enforced as such.

Often, they are nothing more than suggestions.