Jobs and gigs have attributes associated with them, while only jobs have perks. Each attribute defines a specialization within the job's overall playstyle.
For example, the Chemist is a potion-throwing, item-combining class. His perk is Cognate Sciences, which makes his gig's attributes more effective, and his attributes are Pharmacology for healing and cures, Toxicology for poisons, and Material Sciences for explosives.
Each perk and attribute is associated with a set of skills. You can increase and decrease their values in safe areas (no permanent decision), and their skills' effectiveness with scale with their attributes.