A role is considered to be Limited Use if it cannot be used freely throughout the game. A Moderator will often make explicit how many times a player can perform their role through phrases such as "one-shot" or "two-time use." For instance, if a role is "one-shot," that means a player can only perform it one time before it's gone, leaving the player functionally as your average, everyday vanilla or goon.
The most common role to receive limitations are Vigilantes, since a player killing too much can cause a game to become unbalanced. Other common one-shot roles include: Bulletproofs, Jacks of All Trades, Skitzos, and Hitmen.
Oftentimes if a player performs a limited use action, and the action fails to effectuate (e.g. the person the Vig shot was protected by a doctor), then the action is considered to have "happened" and thus is expended. But if a player was roleblocked, then arguably the action never happened at all, and thus the player can still perform it later.