Atomicity :- A transaction is a unit or work in which a series of operations occur between the BEGIN TRANSACTION and END TRANSACTION statments of an application. A transaction executes exactly once and is atomic - all the work is done or none of it is.
Consistency :- A transaction is a unit of integrity because it preserves the consistency of data, transforming one consistent state of data into another consistent state of data.
Isolation :- A transaction is a unit of isolation allowing concurrent transactions to executes and isolate one transaction from other transaction.
Durability :- A transaction is a unit of recovery. If a transaction succeeds, the system gurantees that it updates will persit, even if the computer crashes immediately after the commit.