Trait

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.

Effect
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 (with the lack of traits in Fallout 3, some perks do have negative effects). 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 his traits. Note that if you chose no trait at character creation, you cannot fill the empty slot with this perk.

Race
In Fallout Tactics, where characters of different races can be created, traits also have different racial requirements.

Old World Blues traits
Traits added by the Fallout: New Vegas add-on Old World Blues.
 * Claustrophobia
 * Early Bird
 * Hoarder
 * Hot Blooded
 * Logan's Loophole
 * Skilled

Racial traits
Racial traits only appear in Fallout Tactics.
 * Beta Software
 * EMP Shielding
 * Domesticated
 * Fear the Reaper
 * Glowing One
 * Ham Fisted
 * Rabid
 * Targeting Computer
 * Tech Wizard
 * Tight Nuts
 * Vat Skin