Perks are bonuses obtainable by the player character or companion in the SPECIAL character system. The number of ranks each perk has determines how many times the perk can be obtained. In contrast to traits, perks are almost purely beneficial with only some exceptions.
A character's perk rate determines how often the player character gets to choose a new perk (or an additional level for an already obtained one). In Fallout, Fallout 2 and Fallout Tactics, the player character can choose a perk every three levels, with Fallout Tactics offering different rates for non-human characters. When choosing the Skilled trait, the perk rate is reduced so that the player character can choose a perk every four levels. In Fallout 3, Fallout 4 and Fallout: Brotherhood of Steel, the player character gets to choose a perk (or skill) at every level. In Fallout: New Vegas, the perk rate is set at every 2 levels.