(1) For optical fibers, see 
bend-insensitive fiber.
(2) (
Binary 
Interchange 
File 
Format)  A spreadsheet file format that holds data and charts, introduced with Excel Version 2.2 in 1989.
(3) A novice on the Usenet bulletin board.  Also spelled "B1FF," a BIFF is a newbie who tries to be "cool" by, among other things, abbreviating words with clever misspellings.  See 
Usenet and 
leetspeak.