In computer science, ACID (Atomicity, Consistency, Isolation, Durability) is a set of properties that guarantee that database transactions are processed reliably.
Atomicity: requires that each transaction is "all or nothing": if one part of the transaction fails, the entire transaction fails, and the database state is left unchanged.
Consistency: Ensures that any transaction will bring the database from one valid state to another.
Isolation: The isolation property ensures that the concurrent execution of transactions results in a system state that would be obtained if transactions were executed serially, i.e. one after the other. Providing isolation is the main goal of concurrency control. Depending on concurrency control method, the effects of an incomplete transaction might not even be visible to another transaction.
Durability: Durability means that once a transaction has been committed, it will remain so, even in the event of power loss, crashes, or errors.
See also, if You wish or need ... : Transactions, Source.