Medians systems are people between the spectrum of singlet and multiple, which is to say they are neither fully singlet, nor fully multiple.
A median is thought to be by some the midpoint between singlet and multiple. There are other ‘people’ sharing headspace but they are all facets or aspects of one core person. They are distinct but not truly ‘separate’. Being median is a sort of fuzzy state between being singlet and multiple; they’re kid of a single identity made up of multiple ‘selves’.
I don’t personally experience being median, so I can’t really share any personal insight.