What is a delegated administrator in Salesforce and what are its duties?

In Salesforce delegated administrators can do following duties:

1. Create and edit users in specified roles and all subordinate roles.
2. Unlock users.
3. Assign users to specified profiles.
4. Assign or remove permission sets for users in their delegated groups.
5. Create public groups and manage membership in specified public groups.
6. Log in as a user who has granted login access to the administrator.
7. Manage custom objects.