What do the initials bt stnad for?

British telecom.

'BT'

British Telecom (Corporation)

Bit Torrent (form of Peer-to-Peer file Sharing)

Brian Wayne Transeau (Musician)

Bacillus Thuringiensis (natural insecticide)

Perhaps if you were a bit clearer on what it is you're asking about,

the could be more clearly defined. Thank you.