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

Thread copied to the What are M-Theory and String theory etc. and are they valid scientific theories? thread in the Is It Science? forum, this copy of the thread has been closed.