ACID stands for Atomic, Consistent, Isolation and Durable
Atomic (A) - A transaction consists of many operations. All operation in transaction succeeds or every operation is rolled back.
Consistent(C) - After transaction completes, database must be in consistent state. A transaction can bring one consistent state to another consistent state.
Isolation (I) - There can be many transactions in the system executing concurrently but each transaction execution is isolated from another and looks like they were executed in sequential order.
Durable(D) - The result of applying transaction is permanent even in the presence of failures.