A.C.I.D.

• Atomic - Every operation in the transaction succeeds or else they all fail.
• Consistent - Ensures that the database state is valid at all times.
• Isolated - Ensures that concurrent transactions (i.e. from different connections) occur as though they were executed serially.
• Durable - Once commited, changes are permanent.

Database transactions usually satisfy the A.C.I.D. properties (for example, in PHP).