ITM: In the money (finishing in a tournament high enough to win prize money)
IWTSTH: "I want to see that hand" - refers to a controversial and often poorly-understood rule in brick-and-mortar play allowing some or all players at the table to ask to see a calling hand, not just the called hand, at showdown.
MUBS: Monsters Under the Bed Syndrome. Because, in poker, one cannot see an opponent's cards some players tend towards picturing the worst case scenario even if the cards required are an unlikely holding. A player who is prone to assuming an opponent has such cards is fearing MUBS.
SNG/SnG: Sit-and-go, single table tournaments that begin when enough players are seated.
SOSA: Show one, show all
STT: Single-table tournament. Often the same as SNG.
T$: PokerStars Tournament Dollars. These are accumulated by winning your way into a tournament and then unregistering. They can be used to register for other tournaments. These can also be sold to other players.
VP$IP (often shortened to VPIP): Voluntarily put money in pot. See PokerTracker docs for more details.
W$: PokerStars "W" Tournament Dollars. These are accumulated by winning your way into "W" tournaments such as WSOP qualifiers, WPT qualifiers and WCOOP tournaments and then unregistering. They can be used to register for other "W" tournaments. These can also be sold to other players.