In science fiction and fantasy, a Big Name Fan (BNF for short) is a member of a fandom who is particularly well-known, liked and celebrated for their contributions of art or fanfiction to the fandom. They generally have many followers (often called fangirls), who praise them and read their online journals, but rarely receive a reply back from the BNF.
BNFs are so admired that people ask for autographs at conventions and pay them to speak as guests. One cannot proclaim oneself to be a BNF, to do so would be to invite laughs of derision, since it is a term of admiration which must be applied to you by others, if at all.
Most BNFs are simultaneously hated and loved in the fandom. The title BNF also carries a negative connotation of being arrogant and self-important.
A good example of a BNF is Cassandra Claire, who is a BNF in both the Harry Potter (for the Draco Trilogy) and the Lord of the Rings (for her Very Secret Diaries) fandoms.