1  –  CASCADE

    The CASCADE clause drops the specified user from the database
    and deletes all references to this user that exist in the access
    control lists (ACLs), modules, and schemas. If the PUBLIC user is
    dropped, ACLs are not processed to remove the PUBLIC entry.

2  –  RESTRICT

    The RESTRICT clause drops the specified user. If there are
    any references to this user in another ACL, then the DROP USER
    statement fails.

    The RESTRICT clause is the default.

3  –  username

    An existing user name in the database.