A set of properties ensuring reliable processing of database transactions. Still applies to structured portions of multimodal systems.
When a transaction starts, every operation follows the ACID rules. If something fails, the database undoes any partial changes to avoid corrupt data. If everything is successful, all the changes are saved. This approach prevents data from getting messed up.
Behind the scenes, database engines use logs, locks, and close coordination to enforce ACID. They keep track of each step to make sure every change either happens completely or not at all. They also isolate concurrent transactions from each other and guarantee that changes aren't lost once committed.