ROLLBACK is a command that execute at the end of current transaction and undo/undone any changes made since the begin transaction.
but Aborting means a transaction that consists of ensuring that state of the database becomes as if the transaction had never begun. Any changes made by the transaction must be undone and we must ensure that those changes had no effect on any concurrently executing transactions. during this stage we can kill any process/transcation which is not used for longer time.