A queue is known to be one type of message that will be sent to only one subscriber. A topic is something that will be sent to different subscribers. There are times when you only want to send one message to just one person, especially if the message is private and you do not want other people to know more about it.
For this particular scenario, the topic is usually sent from the publisher to subscriber while queues typically point to point. Let us say that you are a subscriber to a particular network. Whenever the system sends notice, you will be one of the subscribers who will receive a message.