Definition: ACID

(Atomic, Consistent, Isolated, Durable) The properties of a transaction in a well-designed database management system (DBMS). The transaction must be ATOMIC (all updating tasks must be completed or nothing is done), CONSISTENT (it cannot leave the database in a state that violates any integrity rules), ISOLATED (remain invisible to other operations until completed) and DURABLE (will complete or be reversed if the system fails in the interim).