What is durable subscription?

To ensure that a pub/sub application receives all published messages, use PERSISTENT delivery mode for the publishers. In addition, use durable subscriptions for the subscribers.
A durable subscriber registers a durable subscription by specifying a unique identity that is retained by the JMS provider. Subsequent subscriber objects that have the same identity resume the subscription in the state in which it was left by the preceding subscriber. If a durable subscription has no active subscriber, the JMS provider retains the subscription’s messages until they are received by the subscription or until they expire.