Types

Traumagenic: A system that formed due to outside trauma; one of the two most prominent formation categories. There are no restrictions on the type of trauma that can cause a system since trauma is highly subjective depending on the specific person.

Endogenic: A general term for systems that did not form due to trauma; the second of the two most prominent formation categories. Many other types of system formation fall under this category. Whether a system chooses to use those specific definitions or simply endogenic is their decision.

Parogenic: A system that was intentionally formed by imagining a person within the mind and treating them as a real person until they branch off and gain independence. This term can also be known as 'tulpamancy', though since this word has religious and cultural significance, parogenic is more widely suggested for systems.

Neurogenic: A system that formed due to pre-existing conditions. Oftentimes, other mental illnesses or neurodiversities can cause this type of system. For example, autism has been believed to have an influence on plurality, as autistic people appear to be more likely to be plural systems than the rest of the population. Any mental illness or neurodiversity can influence a system and be considered under the neurogenic label.

Protogenic: A system that has been plural throughout the entire life of the body. Systems who identify this way believe that they were born this way or have been plural for as long as they can remember.

Paragenic: A system that formed due to experiences with maladaptive daydreaming. This could also fall under the umbrella of neurogenic, and it's up to the system in question to decide if the term is fitting for them personally or not. 

Pariogenic: A system that consists of soulbonds in whole or in part. Alternatively, this can be called a soulbond or gateway system, and the specific term is up to the system that may or may not choose to use it. 

Quoigenic: A system that intentionally chooses to not disclose their origins. This could be for a variety of reasons, but once again, this is the choice of the system at the end of the day. 

Adaptive: A system that originally formed due to a reason unrelated to trauma only to later shift functionality to cope with outside adversity. A system of this type could choose to identify as the specific type of initial origin, mixed origins, or simply adaptive. 

Mixed Origins: A system with multiple factors that played a part in their formation as plural. Any combination of types of origin can play a part here, and it's a system's choice individually whether or not they choose to disclose these various factors. 

Cryptogenic: A system of unknown origins. Systems that do not know how they form or do not wish to learn the truth may use this term. This could also be used for a system that could also fall under the quoigenic category. 

Polyfragmented: A system with many members. The definition has fluctuated with time, but most cite it as a system with 100+ members.

Questioning: Someone questioning whether or not they are plural. 

Multiple Personality Disorder (MPD): A disorder that was previously diagnosed on anyone who showed signs of having multiple identities living within a shared body. This term is frowned upon at present due to its inaccuracy and stigma, and the disorder's label has been retired for over thirty years. These days, this diagnosis has been replaced with DID.

Dissociative Identity Disorder (DID): A dissociative disorder with (1) distinctive headmates and (2) gaps in the memory between switches. This, much like OSDD, can only be diagnosed if a system is in chronic distress or disorder due to being plural. If the other two criteria are present but there is no distress, no diagnosis can be made. 

Other Specified Dissociative Disorder (OSDD): A disorder similar to DID but lacking in one of the two primary diagnostic criteria. Distress or disorder must be present for a diagnosis.

OSDD-1A: A dissociative disorder with firm amnesiac barriers between headmates, but the headmates are much less defined and are often viewed as facets of a single identity. 

OSDD-1B: A dissociative disorder with distinctive headmates but no amnesia between switches. The memory pool is continuous and easier to access. 

Partial DID (P-DID): A dissociative disorder characterized by a primary headmate being in control most of the time with others influencing to a lesser degree without fully switching with the main fronter.

A common misconception regarding systems is that in order to be diagnosed, the system's origin has to be traumagenic. Many believe that DID or OSDD can only be diagnosed if a system experienced repeated trauma throughout early years of childhood, thus making the system traumagenic, but this is not the case. Trauma is not part of the diagnostic criteria; distress is the closest requirement to trauma here, but they are still distinct concepts. A system can be endogenic and still be diagnosed with DID or OSDD. According to the DSM-V, childhood trauma may be a factor that influences the likelihood of being a system later in life, but since causes of plurality are still unknown, this is only a hypothesis. Another major indicator of a dissociative disorder is disorganized attachment, or an insufficient support system during a stressful time for a child. Trauma is highly correlated with dissociative disorders, but they are not always one and the same. Traumagenic does not exclusively mean disordered. A system can be disordered (a label that is difficult to pin down in and of itself) and not be traumagenic, and a system can be non-disordered and still be traumagenic. Disordered does not equal traumagenic, and this has never been the case. Beyond that, DID and OSDDD are not trauma disorders by definition; they are dissociative disorders, and even if they are associated with trauma, that does not mean they are inherently caused by it.