Mafia is a game controlled by a host. Each player is assigned secretly to a character by the host.
Most generally, Mafia games consists of two teams:
- the "uninformed majority" - the good guys, the townspeople, who cannot communicate with one another - in fact, they don't know any identity but their own. Usually called Innocents or Goodies.
- the "informed minority" - the eponymous Mafia, the bad guys, who know each other and can engage in BTSC - "behind the scenes communication" in a host prepared environment. Usually called Mafia or Baddies.
The Game consists of alternating cycles of Night and Day (starting with Night 1 in most games):
- During Night, the Mafia kill off one innocent villager (nightkill)
- During Day, everyone votes on one unlucky person to be "lynched" (lynch=publically executed).
So, in essence, Mafia is a game of elimination. The last team left standing wins.
It's actually a little more complicated and interesting than that. Each player -- in addition to belonging to a team (faction) which has a goal in mind (often based around killing off the other team/s) -- has their own individual identity, called a role. Each role usually has some kind of ability/property.
- a Doctor can choose 1 person per night to stand by and save in case that person is targeted by the Mafia.
- a Spy can choose 1 person per night to investigate and learn the identity of.
For more specific information, one must read the game that they are playing. The game design will outline the teams and the roles on each team, and most of the rules as well as preferences of the host (for example, what happens in the event of a tie in the daily vote of who to kill).
For a more detailed outline of the game of Mafia, one must read the Newbies' Guide to Mafia.