BIC
Back In Character - Sometimes used preceding a statement or description from a character's point of view after making an OOC statement.
Godmodding
A term to describe someone who roleplays a character with the the ability to avoid all potentional character-damaging, fatal attacks or any boon that should have happened to a character during roleplay.
IC
In Character - Sometimes used preceding a statement or description from a character's point of view.
Metagaming
A term to describe someone who uses knowledge gained out of character and not obtained in character or within the storyline.
NPC
Non-Player Character - A character that's not actually played by a person participating in the game but a character in the actual storyline.
OOC
Out of Character - Mostly signified when you're speaking out of character in the middle of a roleplaying. Sometimes used preceding a statement or description when breaking out of roleplaying to ask a question or make a comment.
Powergaming/Powergamer
A term to describe someone who roleplays a character with too many/much/powerful magic, abilities, or skills defined by one with authority.
RP
Role Playing