heatware = peer ratings for trading, all hosted on a lovely website. Somewhat like e8ay feedback.
BM = brick and mortar (physical store, not online or virtual)
TTT = To the top, a common bump saying
bump = to push the message 'to the top'. In this forum system, everytime a message is replied to, it goes to the top of the list.
PM = private message *or* price match. Some storews will match other stores prices. This is obviously useful when you can match a price at one store that offers coupons . . .
YGPM = aka YHPM, you got private message or you have private message
MIR = Mail in rebate.
Troll = someone who tries to con other people out of their money, usually done on the FS/FT forum.
AT = anandtech or an older form factor for a motherboard.
OC = overclock
Borg = check the distributed computing forum . . .
that's all i can think of off the top of my head.