BNF stands for Big Name Fan, a fan of accomplishment who is extremely well known throughout the microcosm. Typically active in more than one aspect of fandom, BNFs are larger than life characters whose contributions to fandom merit high recognition.

In rare cases, strength of personality alone has been enough to make someone a BNF, and sheer longevity may do it, but it generally takes something extra to rise above WKF. BNF is always positive. The initialism doesn't apply to famous fuggheads. Nor can you claim BNFhood for yourself — to do so invites derision — it's a term of admiration which must be bestowed by others.

The term was originally used satirically by Charles Burbee to mock those who took fandom too seriously, but within a short period became an accolade. It is becoming archaic and limited to descriptions of bygone fen. Fans seldom describe others as BNFs anymore, perhaps because fandom has become so large, amorphous and diverse that no one can be very well known throughout.

Contributors: Dr. Gafia, others.

from Fancyclopedia 2 ca. 1959
Big Name Fan. One of importance and influence in fandom; well-known and with a solid reputation. Fans who last long enough or are active enough eventually find that their names are known to other fen all over the country. The status is usually achieved by participating in fannish affairs for a long time, or publishing a top fanzine, producing quality writing and/or illustration, or in any number of ways which keep one's name before the fans in a responsible manner. The term must be earned; it cannot be appropriated or purchased (Acts 8:18-21), nor conferred on yourself or your friends. When newer fans gasp in awe on seeing you, you are a BNF. If they just gasp period you're making progress.