There is a repository of sorts in the moderator area where threads or individual posts can be stored if we choose not to delete them entirely and forever. I dislike making things just "disappear" so occasionally I show the "Thread has been moved" tag just because there isn't a way to leave a message that the thread has been deleted. In this case, I intended to edit out the bad parts and leave the thread intact, but when I went in to edit it, there was much more work to be done than I had time to wade through.
So, it gets moved to storage. In the event that there was really good content in the thread and we get several requests to bring it back, then it gets put on a list until one of the mods has some free time to edit out the bad and leave the good.
That's also another reason that things get moved. Sometimes we know that a thread has valuable content that we want to save, and other times there's been a complaint and a mod might want to confer with the other mods and admins to reach a consensus of opinion before something gets deleted forever. In those cases, it gets "moved" to storage rather than deleted so that it can be brought back if we decide on that course of action.
Does that help?