I don't define/explain the term theory. The Scientific Method does that for all true scientists. If you truly don't know, then I would suggest you find a good link or book on the Scientific Method. It would be possible to post it here, but I prefer not to waste time and space doing so. If you wish, I could freepmail a good discussion of the Scientific Method to your personal mailbox.
W.K.
Books on scientific method are, at best, just descriptions of what scientists do. At worst, they are just philosophers' wet dreams. Scientists in general never consult philosophers about what they should be doing.
Science does not seek truth. It seeks knowledge. There is a difference. Knowledge is always incomplete and tentative. Knowledge has the attributes of utility and degrees of confidence, but never has certainty and logical perfection.