BB is an extension given to files associated with a programming language called Blitz. BB files are used to store source code written in that language. For Blitz, this is the default format. Technically, it's a plain text file that can be opened in any editor. Blitz is based on the BASIC language and was developed for computer game development.

The author of the first Blitz BASIC compilers was Mark Silby. Currently, the BB format is rare and considered obsolete.