There are a lot of words you hear associated with plurality, in unusual ways. Other people on the internet may disagree with our usage of these terms, and that is okay. This is just how we use them.
Plural / Multiple – a state of having more than one person/consciousness in a body.
Singlet – someone who is not part of a plural system; a single person in a single body.
System – a neutral term referring to a body that is plural. Or more precisely, to the group that resides in it.
Gateway System – a specific kind of system where the people who front are residents of an inner-world/other-world.
Headmate / Systemmate – A member of a plural system. Please don’t use the words “alter” or “personality” unless someone explicitly tells you to do so.
Inner-world / Other-world / Headspace – A place that members of a system may reside and/or visit. “Inner world” and “headspace” are more common in the larger community, but we like “other world” because it doesn’t have any implication about where it’s located.
Front – Control over the shared body. This act is called “fronting“. Likewise, you may have “co-fronting“, where there is more than one.
& – This isn’t exactly vocabulary, but it is becoming common. It is a way to form a plural from something that is not usually explicitly plural, like “you”. “How are you&?” implies asking how everyone is doing. Likewise, signing a message “- Fuzzy&” might imply, “Fuzzy and others”.
DID/MPD – These are psychiatric diagnoses for someone who is plural, usually by way of trauma. Many visited a doctor/therapist because of feeling disordered or dyscommunicative, but not all of them are.
It is a common misconception that all plural systems fall under this category, but many do not. In general, being a disordered system with broken communication and responsibilities is something that needs help/therapy, not simply being plural. It is the same as with any group of people who must live together. (There are other reasons for plural systems to need help, but I am not going to dive deep on that topic here.) But imagine how ridiculous it would sound if someone suggested that anyone who lives with someone else needs help in a major way.