a database transaction is a collection of database queries running as a single unit (Atomic) in which if any of the queries fails to hole transaction will be rolled back and database will be in the state that transaction never started. the transaction in a database run Isolated and if many transaction run concurrently it's the result is same as that the transaction are executed serially. after a transaction finished the database should be in a valid state and all the database constraints should not be violated.(consistency). after the transaction finished the changes will be permanent in the database even if a power loss or hardware failure occurs (durability).