I guess you ask about deleted "members".
Banned members didn't follow the rules and had their account banned. it's a staff decision.
Deleted members requested that their identity get "unlinked" to their forum's content. it's the right to be forgotten on the internet. if you think your past actions would badly influence or affect your life (finding a job, for example, and they could get back to your content. some users used their real names when registering instead of nicknames!) then you have the possibility to ask to be deleted.
The account is closed (you can't log anymore!), the name is replaced with a generic one, but the posted content is kept (for historical and legal purpose), and to prevent disruption of existing discussion flow and important posted information (guides, tutorials, etc.).
You can also ask to change your name, instead of fully deleting and losing access to your account, if you still want to use the forum.
name change is accepted on a case by case basis, but if it's for privacy reason because you registered using your real first and last name, this is automatically granted!
