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 ActiveMQ (AMQ). Subscribers (e.g. the YOUnite UI) use the STOMP protocol to register listeners. Other JMS protocols should work with YOUnite MDM.