A transaction is a single unit of work, which either has to complete the whole work or roll back to its previous state. A transaction can't stop in the middle of a piece of work. It's a very important feature for sensitive data-handling. One of the best uses of transactions is when dealing with money-transfer processes. When a person transfers some money to another person's account, if any error occurs in the middle of the process, the whole process should be cancelled, or rolled back.

There are four properties of a transaction in SQL: Atomic, Consistent, Isolated, and Durable (ACID).