The forum was originally located at bitcoin.org/smf, then later forum.bitcoin.org, then finally bitcointalk.org. IIRC, Satoshi left before the forum was moved from bitcoin.org/smf. The name "BitcoinTalk" was not invented by Satoshi, Sirius, Gavin, justmoon, or myself. I wonder if anyone here can guess who came up with the name? 
I believe U chose the name and it is inspired by WebHostingTalk, the largest web hosting discussion forum on the internet.