I call the experience of less than distinct/mid continuum identity alteration "gradience." median system is rooted in the endogenic community while using clinical terms from the CDD literature is connected to a traumagenic origin; I like gradience as a general system term.
I made a flag for systems who identify with gradience in someway; their whole system may feel like a gradient system, or they may be a system who experiences gradience and identifies with that even though they also experience themselves as having fully distinct alters. Gradience is frequently (if not universally) experienced by systems, even those with fully distinct alters and amnesia.
The experience of gradience can be broad. It has been described in many different ways. Less than distinct alters tend to feel like they are distinct yet but distinct enough to feel fully autonomous or separate. Can feel like different modes, different versions of one self, different roles, a strong emotional state, or an identity with many/variable distinct aspects but with no clear division between any of them. People with distinct alters can experience gradience within their alters or specific parts of their system.
The endogenic community coined the term median system to describe this situation. It is possible to be median in parts of a system instead of an entire system, or for system functioning to be more or less median over time. It is possible to have a central identity or no central identity.
In the CDD literature, gradience is referred to as "less than distinct identity alterations." these less than distinct indentities may or may not have amnesia associated with them. This identity fragmentation could be secondary to: CPTSD, OSDD, PDID, personality disorders, and even people with DID can experience gradience alongside their experience of distinct selves (this is very common.) common presentations of gradience include:
DID subsystems where an alter has a system of less than distinct selves inside.
Fragments in polyfragmentation.
OSDD1 presentations where alters have amnesia but don't feel distinct.
PDID presentations where alters feel less than distinct or feel less than distinct because they cannot take executive control.
Personality fragmentation in CPTSD.
Personality fragmentation in PDs.
In IFS therapy, people are trained to see themselves as these different parts of the self, this internal family, that has distinct wants and needs. From what I can tell talking to people without a DD who use this, they do feel like the IFS states are real, distinct, and semiautononous facets of themselves, but they feel like they are parts of one whole. I have heard of some people coming to view themselves as systems after learning IFS. For those who don't see themselves as systems but use it, this is a good example of gradience in singlets - the other end of the plurality spectrum from multiplicity.
Gradience in System Dynamics
Gradience can also be used to describe system functioning and not just system members. Gradience in system dynamics refers to things like how opaque and frequent amnesia is; how difficult co con is and whether they lose time during co con; how often they have identity blurring (where fronters feel like a mix of alters that are usually separate); how easy it is to share things like feelings or ideas or skills between alters; how easy internal communication is; how much power different alters have to influence the system or internal world or control the body.
Also on a related note: never feel pressure to decide if you are more or less distinct. I prefer thinking of gradience as something all systems experience in varying degrees.
Second note: I am sure there are many similar terms and ideas that may have slight differences in nuance. This is how I think about it. Feel free to use my conceptualization.