Terms that describe who or what members are; such as "little" or "fictive." These are usually involuntary, but as with everything, differs from person to person.
Note: for terms more focused on jobs and duties, see system roles.
Age Slider: A person whose age varies, changes, or "slides" at different times. Is not the exact same as (SFW) Age Regression, but for some, they're considered the same thing.
Big: A name for adult/older system members, sometimes a term used just by littles but may vary between systems.
Little/Syskid: A young system member, commonly up to 12 years old.
Lost Adult: Bodily in headspace, they look like an adult and identify with older ages, but mentally they think more like children. Someone with a "stunted" age, who physically grew up but mentally did not.
Middle/Systeen: A teenage system member.
Introject, or introtive, is a term to describe system members who originate or are based on an outside source.
Aesthetive: an introject of an aesthetic personified (eg cottagecore, clowncore, vaporwave, etc)
Amitive: An introject of a member of another system, usually a system that is close to you but not always.
Factive: An introject of a real person.
Faitive/Fucktive/Fcktive: An introject in between a real person and a fictional source.
Fictive: An introject from a fictional source.