Perk

In the SPECIAL character system, perks are bonuses obtainable by the player character or companions. 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.

In Fallout: Brotherhood of Steel, "skills" have the same function as perks in other Fallout games. Conversely in Fallout 4, the perk system expands to replace skills.

Regular perks
The most common perks, selected during a level up compared to the perk rate. They are classed by level or point required, and generally have stats 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 your Endurance statistic.

Challenge perks
Perks obtained as a reward for challenges.

Unarmed perks
Perks adding special unarmed moves.

Companion perks
Perks related to a companion and affecting the party as a whole. The perk disappears if the companion is no longer in the party. Can require a good relationship with said companion.

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

Perk rate
A character's perk rate determines how often the player gets to choose a new perk (or an additional level for an already obtained one). In Fallout, Fallout 2 and Fallout Tactics the player 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 can choose a perk every four levels. In Fallout 3, Fallout: Brotherhood of Steel, and Fallout 4 the player gets to choose a perk (or "skill") at every level. In Fallout: New Vegas, the perk rate is set at every 2 levels.

List of perks
Lists of perks for each game can be found on these pages (also listed above):
 * Fallout perks
 * Fallout 2 perks
 * Fallout 3 perks
 * Fallout: New Vegas perks
 * Fallout 4 perks
 * Fallout Tactics perks
 * Fallout: Brotherhood of Steel perks