In JMS, a topic implements publish and subscribe semantics. When you publish a message it goes to all the subscribers who are interested - so zero to many subscribers will receive a copy of the message. Only subscribers who had an active subscription at the time the broker receives the message will get a copy of the message.
The default JMS provider for YOUnite MDM is Apache ActiveMQ (AMQ). Subscribers (e.g. the YOUnite UI) use the STOMP protocol to register listeners.