A transaction is a single unit of work. If a transaction is successfully executed, all of the data modifications made during the transaction are committed and become a permanent part of the database. 

ACID is the acronym for Atomicity, Consistency, Isolation, and Durability.

1. Atomicity means that the transaction will succeed, as one unit, if all the separate tasks succeed with no issue. On the other hand, the failure of any single task within this transaction leads to the overall transaction failure and rollback. 
2. Consistency guarantees that the transaction will not affect the database consistency and will leave it in a valid state by complying with all database rules, such as constraints and foreign keys, defined on the columns.
3. Isolation means that each transaction has it is own boundary, that is separated from the other concurrently executing transactions, and will not be affected by these transactions’ operations.
4. Durability means that the result of the committed transaction that is written permanently to the database will not be lost even in the case of any abnormal system termination or failure, as there should be a mechanism for recovering this data.