The Town is the collective group of players that are trying to eliminate the Mafia and other Scum factions from the game. The adjective "townie" is used to describe a player who is aligned with the town, or is otherwise playing a solid town game. By far, most players in a game are townies, however being that they typically do not know anyone else's alignments initially, they are considered the "uninformed majority." The Town's most useful method of taking out the Mafia is the daily execution. It is important for all townies to use carefully their reason, wits, gut, and (most importantly) votes towards executing the Mafia.
The Town typically has a number of roles at their disposal, such as Cops, Doctors, and Vigilantes, to make it easier for them to catch the Mafia. Townies without powers are called Vanilla Townies, as they are "plain."
The word "Town" is also often used to describe all the players of the game collectively, since they are all part of "a town." It should be clear from context whether the speaker means Town as in the town-aligned players, or Town as in the players of the game.