ABSOLUTE CINEMA

based on this:

For starters, if you're looking into systems, you'll probably run across the term "plurality", which is an overarching term that refers to all instances of someone sharing a body/brain; it is the state of being more-than-one, not just an individual collection of beings in a single body (the latter is what the word "system" specifically refers to). There's also the word "plural", which can be used either as a noun to mean the same thing as "system", or as an adjective to describe things that involve or exhibit plurality. For instance, I am plural. I very much enjoy talking about plurality and plural characters in fiction.

(As a comparison, you may think of video chats/group calls. Plurality, here, would be video chats in general. Meanwhile, a specific video chat – called a webinar – would be a system. And the people in a webinar would be the members of a system. Or, for another example, plurality would be education, a system would be a class, and the members of that system would be the students.)

Speaking of, beings who share a body – who are part of a system – are called many different terms. Two of the most common are "headmate" and "alter", although I also see "system member" a lot. I could say that my headmate was rather helpful today, or that my alter was fronting yesterday. Alter is more medical of a term, but it's more standard, especially in some other languages outside English.

But, wait, you might be wondering what fronting is! Well, since we all live in the same body, we've got to share control of it too, don't we? Fronting is what we call controlling the body, and switching is when we change who is in control. Some systems switch often, while others switch rarely, or only under certain circumstances, and some systems never switch at all. Switching may be involuntary, or it may be a voluntary skill a system has picked up. There's a lot of variety across systems.

Plurality is most often known in the context of DID, or Dissociative Identity Disorder, which often involves a lot of involuntary switches. P-DID, or Partial Dissociative Identity Disorder, meanwhile, involves very few switches, but these are likely to be involuntary, as well. There are other disorders that plurality may be a part or symptom of, but plurality can also exist as its own non-disordered state, so long as there's no attached or related issues causing problems for the system (ex. memory issues are another frequent problem in DID, and these memory issues come from the members of a system not remembering what the others did when those alters were fronting).

You may be wondering, how does this happen? How does someone become a system? There are many different ways. Sometimes, it's a part of someone's culture, religion, or spirituality. Sometimes, it's the brain's response to trauma, trying to protect itself. Sometimes, someone is simply born this way. Sometimes, someone may become a system out of the blue, or cause their own plurality somehow. Some systems have a multitude or mix of origins. Most studies on systems currently focus on systems that originate from trauma, as these systems most often have issues – including the trauma in question – that need to be looked into and addressed, but there are some budding studies into systems with other origins, such as the few current and ongoing studies on created systems (the aforementioned systems that cause their own plurality).