The word "mafia" is a generic term commonly applied to organized crime groups around the galaxy, usually those that deal in the shadows and specialize in extortion (especially protection racketeering). Mafias often claim sovereignty over a territory, which can be as small as a neighborhood and as large as multiple star systems. The largest mafias can have a presence on hundreds of worlds.
Notable mafia groups
One of the most notable mafias is the Bright Ebony Organization, which controls the Prakuul system and a few lesser colony worlds near it, and has a presence on dozens of other major planets.