ACID means (Atomicity, Consistency, Isolation, Durability) is a set of properties that guarantee that database transactions are processed reliably.
For any transaction of a relational database system, every task of the transaction will either all completed, or nothing will be completed. The series of tasks for the operation cannot be pended at any point.
For example, if a bank user want to do a payment transfer from one bank account to another bank account. The transaction process for the payment transfer must be completed or never occurred. The Oracle Database has the rollback function and instance recovery to match the Atomicity.
The data in the database have to match all validation rules.
In a relational database system, two transactions are executed at the same time. Both transactions try to modify the same data, one transactions must wait for the other to completed.
For example, the concept of ‘lock’ is good example of the Isolation.
Once the change in a relational database system is committed, the change will keep remaining.