Dissociative Disorder is a category (group) of mental disorders.

with in the group name of dissociative disorder are many different mental disorders..

the mental disorders in this category / group / type of mental disorders called dissociative disorders are:

depersonalization
derealization
dissociative amnesia
dissociative Fugue
dissociative disorders not otherwise specified
dissociative Identity Disorder

each one of these dissociative disorders have their own symptoms and also share some symptoms.