Knowledge base / Lists and subscribers
Unsubscribe vs erase (publishers)
Unsubscribe stops mail and keeps the row. Erase deletes the address and events for that list.
On Subscribers you can unsubscribe someone (status becomes unsubscribed) or purge them (row and delivery events for that list are deleted).
Readers can do the same from the link in every email: unsubscribe, or delete their data. See unsubscribe and delete reader data.