What is Atomicity, Consistency, Isolation, and Durability (ACID)

In computer science, ACID is a set of properties that guarantee that database transactions are processed reliably: Atomicity: Either the task (or all tasks) within a transaction are performed or none of them are. This is the all-or-none principle. If one element of a transaction fails the entire transaction fails; Consistency: The transaction must meet all protocols or rules defined by the system at all times. The transaction does not violate those protocols and the database must remain in a consistent state at the beginning and the end of a transaction; there is no any half-completed transactions; Isolation: No transaction has access to any other transaction that is in an intermediate or unfinished state. Thus, each transaction is independent into it. This is required for both performance and consistency of transactions within a database; and Durability: Once the transaction is complete, it will persist as complete and cannot be undone; it will survive system failure, power loss and other types of system breakdowns. ACID is having the property of Strong consistency of transactions, availability less important.

Considered to be the key transaction processing features/properties of a database system. Without them, the integrity of the database cannot be guaranteed.