WIFOM (Wine In Front Of Me): Any thinking that boils down to "You did X, so you must be innocent. Unless you knew that I'd think that, so you must be mafia. And you knew that I'd do that, meaning you're innocent..." Named for this scene
from The Princess Bride.
OMGUS (Oh My God You Suck): The act of voting or suspecting someone because they suspected you. (I.e.: Alice votes Bob, so Bob says that Alice must be mafia because she voted for him.)
LYLO (Lynch Or Lose): When there is only one more townie than mafiosi and mafia allies during a dayphase. (I.e., 3 townies and 2 mafia. If town Mislynches or No Lynches and lets play go to night, the mafia will win.) The town must correctly lynch mafia on this day or lose.
MYLO (Mislynch Or Lose): When there are two more townies than mafiosi and mafia allies during a dayphase. (I.e., 4 townies and 2 mafia. If the town Mislynches and play goes to night, the mafia will kill and win the game. If the town No Lynches then the mafia will kill and put the game in LYLO.) If the game is known to be in MYLO, most towns will generally vote to No Lynch. It is generally easier for towns to win in LYLO than MYLO.
No Lynch: Voting not to lynch anyone at all during the day.
Mislynch: The act of lynching an innocent player, or the state of being able to lynch an innocent player without losing. (I.e., 5 townies and 2 mafia. If the town kills an innocent and the mafia nightkill, there town will not have lost.)
CC (Counterclaim): When multiple players claim the same role. If a role is CC'd then generally one of the claimers is mafia. This can also be a technique to get a townie to claim and clear themselves (I.e.: 2 vanilla townies, 2 mafia, and 1 doctor. If the doctor claims then there is a leader, but claiming ensures that the doctor will be killed the next night. A townie might claim doctor, let the real doctor CC, and then retract his claim so that the doctor is forced to lead.) PR
(Power Role): Any town-sided role that has a nightaction.
Joint Win: This only applies when the Fool exists (whose win condition is to be lynched). If the fool is lynched and the act of fool dying causes the mafia to equal or outnumber the town, the mafia will also win. (I.e., 2 townies, 1 fool, and 2 mafia. The mafia and the fool can all vote for the fool, lynching him. At the exact moment he's lynched, there are 2 townies and 2 mafia, giving the mafia a joint win with the Fool.)