Stands for "big name fan", as known on tumblr. Within a fandom, there are usually multiple people who are known fandom-wide and who have many more followers than other people. These people are known as "BNF"s.
Evarren was a BNF from klaine fandom before she deleted her blog.
Back and Forth - the daily email loop between a small group of close friends. Typically about nothing. Usually consumes more than an hour or 2 combined. During work hours. Can result in arguments about meaningless topics.
Today's BnF is unreal. I have not done a thing at work except read all these rants on the housing market, golf, NFL, marketing and Michael Irvin.
Acronym for "Beach Noobs Forever"; veterans of Killzone 1 online who played on the map called Beachhead almost exclusively for years on end. Notable members include FAMILYGUY-DEATH, Gs-Criminal, LoCkMaN, BUCKNASTY, WaWaWiiWa and Mazer-Rackham.
Don't make a Core SD, make a Beach DnD and call it BnF.