It probably means to "split" the topic.
I found this in a handbook:
In the Moderator Control Panel, you may split a topic by clicking on the topic title. You will be taken to the Split Topic Control Panel. You may select the posts to split; they will then be removed from the topic and put into a new topic. This will allow you to move off-topic posts to another topic, keeping your topics more organized.
New Topic Title - The title of the new topic created by the split.
Forum for new topic - The forum that the new topic will be located in.
To split only specific posts from a topic, check the box next to each post and click Split selected posts.
To split a post and every post after that one, select the first post to split and click Split from selected posts.