What does ACID stand for in databases?

ACID is a set of properties that guarantee reliable transaction processing: Atomicity — a transaction is all-or-nothing; partial completion is not allowed. Consistency — a transaction brings the database from one valid state to another, never leaving it in an invalid state (constraints are not violated). Isolation — concurrent transactions execute as if they were serial — intermediate states are not visible to other transactions. Durability — once a transaction is committed, it is permanently saved even in the event of a system failure (achieved via write-ahead logging). ACID is the foundation of correctness in relational databases.