Alignment - Who you share a victory condition with. Town-aligned, Scum-aligned, or third party alignments.
Bandwagon - Multiple votes on a single person. Can be justified, or unjustified. Unjustified bandwagons are scummy. Joining bandwagons blindly or without reason is also scummy.
BM - Beginner's Mafia (Or, Bastard Mod, a Mafia game with a purposefully unreliable moderator, or misleading information)
Bus - (noun: the bus ; verb: bussing, throwing him/her under the bus) When a mafia member attacks another one in order to make themselves look like a loyal townie when his or her scumpartner gets lynched.
Cult - A group of players that share a win condition, know each other, and can communicate freely. They are generally a second type of scum, although rarely they can be town-aligned. Instead of a kill, they can recruit players into the cult. There is generally a cult leader, who is in charge of recruiting.
Cycle - The time from a single phase (day or night) to a like phase. From Day 1 to Day 2 is one cycle. From Night 1 to Night 2 is one cycle.
EBWOP - Edit By Way of Post. Since editing isn't allowed in mafia, one may make a second post correcting any errors or missed information in their previous post.
FoS -
Finger of Suspicion, writing someone's name in blue signifies a great deal of suspicion. It's kind of like a fake-vote, or the threat of a vote. Good for getting attention.
FTD - Failure to Deliver, also known as Toaster's #1 Scumtell. The act of promising to post more information at a later time, and then failing to do so. A very difficult action to justify as town, because it means you are either lazy or lying, it is therefore seen as a pretty solid scumtell.
IC - Inexperienced Challenged, players who are too experienced to justify playing in a Beginner's Mafia, and act as mentors/guides for the Town or the Scum.
Lurking - Purposefully not posting, so that you have few or no posts that can be analyzed. Generally a good strategy for scum. However, has the danger of earning you prods, getting modkilled, or found out via Zathras' Lurkertracker. Lurking is different than simply being away or unavailable. A good way to tell if someone is lurking is to check their profile's last active time, and compare it to their last post.
LYLO - Lynch or Lose, a situation where Town only outnumbers Scum by a single person (e.g. 3 town vs. 2 scum). During LYLO, Town MUST lynch Scum or instantly lose.
Masons - A group of town-aligned players who know each other to be town-aligned. They can communicate with each other freely.
MYLO - Mislynch and Lose, a situation where Town outnumbers Scum by two people (4 town vs. 2 scum). During MYLO, if Town lynches Town, Scum will win after night-killing town, making it 2 town vs. 2 scum, which is an instant scum win.
NL - No Lynch, to choose to end the day without lynching anyone and see if any information is revealed in the night.
OMGUS - Oh My God U Suck, a vote on someone else simply because they voted or attacked you
PFP - Posting From Phone (or Profession), throwing up a short post to prove you aren't lurking, when you are too busy at the time to make a more complete post.
PL - Policy Lynch, lynching someone for reasons other than scumminess. Variants are Lynch All Lurkers, Lynch All Liars, etc. Also see: Org.
PPE - Pre-Post Edit, typically done when you go to either Preview or Post and notice that someone else has posted before you. PPE is shorthand for acknowledging the "Warning - You may wish to review your post" message.
RIA - Refuge in Audacity, acting really crazy or really scummy to make people think that you couldn't possibly be scum because of how crazy you are. This never works. Neither does sarcasm in general, really. If you want to be sarcastic, make it painfully obvious you are being sarcastic, with <sarcasm>fake sarcasm tags</sarcasm>. Even still, it's not a good idea, because Mafia is SERIOUS BUSINESS
Role - Also called Power Role, any special powers you have. Cops, doctors, roleblockers, and godfathers are examples of classic roles. Some roles are alignment-specific, some aren't, and some can be for any alignment.
Rolefishing - Any question or attempt to learn information about someone's role. Typically something done at the beginning of the game. Typically a scum move, because it is in scum's advantage to find and lynch powerful roles. Can be acceptable later in the game, or in special circumstances where it is beneficial for town to learn someone's role. The reason it is scummy is because the really powerful town roles want to stay hidden so they don't get lynched by scum, and bringing attention to them by rolefishing risks their secrecy.
RVS - Random Voting Stage, the early-early game, shortly after the game begins, where people randomly vote each other and ask each other different questions, trying to find any good reason to suspect someone.
Scum - Mafia, or someone who isn't aligned with the Town. The Informed Minority.
SK - Serial Killer, a third party role with a nightkill, and who is hostile to everyone.
Survivor - a third party role whose win condition requires that they be alive at the end of the game. Normal players can die and still win as long as their team as a whole wins, but a survivor must actually be alive at the end.
Third Party - an alignment that is independent of scum and town. Has a unique victory condition, and is typically a lone wolf type character.
Town - The anti-Scum. The uninformed majority.
Vanilla - Someone who doesn't have a power role. "Vanilla Town", "Vanilla Scum", etc.
WIFOM - Wine In Front Of Me, the circular reasoning that results from trying to determine the choices of an opponent who acted with full knowledge that his behavior would be subject to scrutiny.
"All right: where is the poison? The battle of wits has begun. It ends when you decide and we both drink, and find out who is right and who is dead."
"But it's so simple. All I have to do is divine from what I know of you. Are you the sort of man who would put the poison into his own goblet, or his enemy's?"
WoT - Wall of Text; a really really long post. Sometimes unavoidable, but generally you should try to keep them to a minimum. Sometimes scum use them to seem more active then they are.
Massclaim - When everyone starts roleclaiming, or saying they are a power role.
Just a human and an Elven civilization in a medium world...
I was much pleased!