What are M-Theory and String theory etc. and are they valid scientific theories?

This is a response to Message 38 by Cavediver in the thread Hawking's Information Paradox solution and Message 40 by Cavediver in the same thread.So, what in fact are the M-theory, String theory and the like? And are they valid science? Do they have any predictable outcomes we should expect? Is there any way of falsifying them at the moment?This thread is for the purpose of educating me and others about what String theory and the likes are about, the evidence for them and if they are considered as science at the moment.If you pull up with some fancy math don't expect me to understand them in any way though

I guess most of us are on holiday now. Don't ruin your holiday time for answering here though

So, I was hoping that Cavediver, whenever you have the time if you would explain how M-theory and string theory are scientific theories and not just some fancy math.I recently watched the whole 3 hours of NOVA | The Elegant Universe | Watch the Program | PBS so I hopefully have at least some basic understanding of these things