Each topic or forum in WSN can have one primary and any number of secondary forums (subject to limits you choose). The versions of a topic/forum which are shown in the secondary forums are called aliases, and are exactly the same as the original.

The advantage of using alias instead of copy/resubmit is that when you edit the topic you will always be editing the original topic and all appearances of that topic will instantly be updated with the new information. (If you had merely copied the topic, you would have to edit each separate instance in each forum.) Also if the topic is suspended or deleted all references of that topic will be removed from the links directory.

To add or remove aliases, edit the topic or forum and see the secondary forums area. Ctrl+click to de-select.