Perk

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.

Regular perks
The most common perks, selected during leveling up, per the Perk Rate. They are classed by level or point required and generally have stat requirements to appear selectable.

Special perks
Perks obtained by special actions or interactions with other characters.

Quest perks
Perks obtained as a reward for quests.

Implant perks
These are perks obtained through implants by an Auto-Doc, which cost money. In Fallout: New Vegas, the number of original implant perks (not those of Old World Blues) you can receive is equal to the player character's Endurance statistic.

Challenge perks
Perks obtained as a reward for challenges.

Unarmed perks
Perks adding special unarmed moves.

Companion perks
Perks which are obtainable by having a good relationship with the respective companions. Companion perks are disabled when not traveling with their respective companions.

Unique companion perks
Perks of a companion, affecting only them.

Legendary perks
Perks obtainable via leveling up past Level 50 in Fallout 76, offering passive abilities, and are able to be ranked up via perk coins, obtained by scrapping unused regular perks.

Perk rate
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.