A median system consists of members who are not entirely separate people, but is not singlet.
Members of a median system may have a common core, as with spokes on a wheel or pages in a book. Each aspect may behave differently, think differently, and have different priorities, but all identify as being the same person. “There are many of us, but we are really all Karen,” is a commonly-cited metaphor. Some people may liken medianhood to being similar to the assumed experiences of a hydra- all share the same base structure, but also have particular individual identities.
Some may consider themselves median if they believe they would not be able to exist without a core or central person existing alongside them.