What is nondurable and subscriber

With an ordinary, nondurable, subscriber, the subscriber and the subscription are coterminous and, in effect, identical. When a subscriber is closed, the subscription ends as well. Here, create stands for a call to TopicSession.createSubscriber, and close stands for a call to TopicSubscriber.close. Any messages published to the topic between the time of the first close and the time of the second create are not consumed by the subscriber. Subscriber consumes messages M1, M2, M5, and M6, but messages M3 and M4 are lost. 

   Nondurable Subscribers and Subscriptions