Plurality

Plurality is the experience of having multiple distinct minds or people that share a single body. You may have heard of DID, or Dissociative Identity Disorder. DID is a form of plurality that involves amnesia between the people sharing the body as well as heavy dissociation that interfere's with daily life. Not plural folks are like DID systems and there's actually a wide range of the ways a system can work. For example, many don't have amnesia and instead share all memories between everyone.

A collective group of people that share a body may be called a system, and individuals within a system may be referred to as system members, headmates, sysmates, or alters. Please note that the term alter has medical connotations and not everyone is comfortable with it. You should always check if someone's okay with the term alter before referring to them with it. 

Fronting

Many systems have their system members take turn controlling the body. This is known as fronting, or being out, and the control of the body may be referred to as front. Someone who is fronting may be called the fronter and changing who's in front is known as switching. Multiple system members can be in front at the same time. This is referred to as co-fronting. Not all systems switch and some systems may not switch at all. Other systems may switch once a year, once a month, once a day, or even several times a day. Systems may have a member who fronts significantly more than the others, or just the most out of everyone else, and this member may refer to themself as the host. 

Member Roles

Some members front to do certain tasks or activities. In fact, some members may have roles or specific tasks. These may be roles that they've chosen to undertake, roles that they feel fit them, or roles they naturally fulfill. Like mentioned above, the host is a role that generally refers to a member who fronts a lot or fronts the most. In some systems, the host may also be the original member or the main member of that system. 

Protectors, like the name suggests, are members that protect the system, the body, or other things significant to the system. They may front during dangerous situations or other situations that require protection. Caretakers are members that take care of the system, the body, or child system members. Persecutors are members who harm the body or the system, often as a misguided or failed attempt to help the system or do what they think is best. It's important to keep in mind that not all persecutors are "bad" or "evil", and they're still people, just like everyone else.

Headspace

What do members do when not in front? This depends on the system. Some systems, or even just specific members, cease to exist or lose consciousness when they leave front. This may be comparable to taking a nap or blacking out. Some just stay co-conscious, which means they're aware of what's happening in front but aren't actually controlling the body. Many systems have a headspace, or a place or world where they go when not in front. This can be anything from a modest cottage to a physics-defying wonderland, and generally can be anything you can imagine. The headspace can range from being just an imagined place to a representation of a system's subconscious to even another world just like this one. Headspaces can also be referred to as inner worlds, otherspaces, otherworlds, or wonderlands. 

Origins

Collective systems or individual members may also have origins, or labels for how they came to be. Discovering and labeling one's origins can help them better understand how they function. There are two main origin labels: traumagenic and endogenic. Traumagenic describes systems or members that were formed due to trauma, often as a coping method. Many traumagenic systems have dissociative disorders such as DID or OSDD-1. Endogenic systems/members did not form due to trauma, although they may have still experienced trauma- it just wasn't how they originated. Endogenic systems and members have a variety of reasons for why they formed. Some believe they formed due to spiritual reasons, while others willingly became plural or were brought to existence willingly by another member. 

There are also systems that have been plural for as long as they remember, often referred to as protogenic systems. Mixed-origin or polygenic systems have multiple origins- these can be any two or more origins and may apply to how the whole system originated or signify that the members in the system have differing origins from each other. Some systems choose not to label their origin or do not know how they originated. These systems might refer to themselves as quoigenic.

Types of Members

There are many different types of members, as well as labels for members based on different aspects of those members. These are different from roles in that they're not something the member performs or does, they're terms to describe what or how the member is. 

Young system members are known as littles, smalls, or middles (the last term refers to pre-teen or teenage members). Similarly, adult system members may be referred to as bigs. Age sliders are members whose age fluctuates or changes; for example, they may be five years old one day, and fourteen the next.

Introjects are system members who are based on existing sources. Introjects based off fictional sources are called fictives and introjects based on real sources are called factives. Introjects don't have to resemble their sources and they might change and differ from their sources. Introjects who significantly diverge from how their source represents them are source-divergent. Some introjects may have exomemories, memories not belonging to the body. Not all introjects have exomemories, and not all members who have exomemories are introjects.

Nonhuman members, as the name suggests, are members that aren't human. They may be inherently nonhuman, have a nonhuman form or body, or are nonhuman in their source. Nonhuman members can be anything, from angels to demons to mythical creatures to normally inanimate objects.

Differences Between Systems

Different systems may function very differently, and it's impossible to pinpoint a standard for a "normal" way to operate as a system. System members may communicate internally, including talking in headspace or sending thoughts to other members telepathically, or they may communicate externally through writing messages/leaving notes for each other. Systems may have from two- or less than two, but more than one- to an infinite amount of members. Some systems share memories between members, while other systems can't access each other's memories at all. 

Some systems do not have inherently independent system members, and members can seem like or be different facets of a single person rather than distinctly different people- however, they are still distinct enough that they aren't singlets, or non-plural people. These systems are called median systems, and systems with distinct, independent members are known as multiple systems or partitionary systems.