BTSC = Behind The Scenes Contact. If you have BTSC, you are allowed to confer with your teammates through private messages and chatrooms outside of the game thread.
EBWOP = Edit By Way of Post. Since you can't edit, this is used to indicate you need to change or add something to a post you just made.
Disco = Discovery Role
LD = Lie Detector
RB = Role Blocker
WIFOM = Wine in front of me (Princess Bride reference) - This is a strategy used by people that are under fire in the thread by saying that "they would never do that."
Switcheroo known elsewhere as OMGUS (Oh My God You Suck) = When a baddie is accused/under fire and turns the tables by accusing the person that's accusing them.
DP = Day Post
NP = Night Post
NK = Night Kill
Linkitis = Briefly, it's a term coined by the Lostpedia forum players which refers to when you post at the same as someone else, rendering your post somewhat irrelevant, or not being in context anymore...or so that you need to respond to people.