The word "BB" is an abbreviation of "Bulletin Board" commonly referring to the php Bulletin Board.

phpBB is a popular Internet forum package written in the PHP scripting language. Available under the GNU General Public License, phpBB is free software.

Some communities have adapted the 'bb' abbreviation at the end of their website to let the community know they are running a bulletin board (usually phpBB).

An informal closing in messages or emails from pagans, Wiccans, witches, and followers of earth-centered religious traditions. Short for the phrase blessed be, a phrase used in greeting and parting similarly to shalom and understood to be short for "May you be blessed by the Goddess."

The lovely fandom of Kpop group DKB (you should stan)

Its a short form of best buds.

Big Brother, the TV show.

Best Babe or Best Bitch