In pre-16.0 databases, there were object-level permissions such as ALTER and SELECT for tables and views, and so on. While statements that grant or revoke these permissions still work, these permissions are now referred to as privileges, but retain the same name.
In addition to object-level privileges, there is a grantable system privilege for every operation that requires authorization to perform. When you upgrade your database, users that had permissions are automatically updated to have the equivalent privileges they need to perform the tasks they could perform before.