It defines a transaction to be a single unit of processing. In other words, either a transaction will be done completely or not at all.
This property ensures that a complete transaction takes a database from one consistent state to another consistent state. If a transaction fails even then the database should come back to a consistent state.
Isolation or Independence
The isolation property states that the updates of a transaction should not be visible till they are committed. Isolation guarantees that the progress of a transaction do not affect the outcome of another transaction.
Durability or Permanence
This property necessitates that once a transaction has committed, the changes made by it be never lost because of subsequent failure.