In the SPECIAL character system, traits are optional character modifications that affect the player character. Traits appear in Fallout, Fallout 2, Fallout Tactics, and Fallout: New Vegas.
Traits modify different aspects of gameplay, such as primary statistics, derived statistics and skills. Traits have positive and negative results, unlike perks in earlier Fallout games. In games where traits exist, one can choose up to two traits when designing a character (or none at all). Choosing the Mutate! perk lets the player change one of their traits. Note that if you chose no trait at character creation, you cannot fill the empty slot with this perk. In Fallout Tactics, where characters of different races can be created, traits also rely on those parameters.
Old World Blues traits
Traits added by the Fallout: New Vegas add-on Old World Blues.
Some traits, such as Bloody Mess and Finesse are also perks for Fallout 3.