NAMI defines

Dissociative Identity Disorder (DID), previously referred to as multiple personality disorder (MPD), is a dissociative disorder involving a disturbance of identity in which two or more separate and distinct personality states (or identities) control the individual’s behavior at different times. When under the control of one identity, the person is usually unable to remember some of the events that occurred while other personalities were in control. The different identities, referred to as alters, may exhibit differences in speech, mannerisms, attitudes, thoughts, and gender orientation. The alters may even differ in “physical” properties such as allergies, right-or-left handedness, or the need for eyeglass prescriptions. These differences between alters are often quite striking.

But what does this really mean? In my opinion and after having lecture on the topic in my Psychopathology class, I understand DID to be a disorder that develops from a previous traumatic event. It seems difficult to understand the disorder in a sense because there are these other alters present in a individual to give some type of relief or a defense mechanism. The average number of alters is about 15 each having their own distinctive characteristics and behaviors.