A system is a set of people sharing one body and brain and acting as a plural group, which may or may not include a headspace. Similar terms for this type of configuration includes “collective”, “family”, or “groups”. A term for a person sharing a body and/or brain with another is systemmate, or headmate.
A system can vary in the type of people they contain, and what each person wants and does. Some systems may be made up of only humans or human-identified people, while others may consist of partially or entirely non-human systemmates. Some may be comfortable staying behind and simply letting other people take control, while others may participate in the outside world.