There’s a difference in philosophy of science between a law and a theory, and it doesn’t have to do with the degree of certainty we have with respect to them. The common sense notion of the difference between a law and a theory is that a law is something we’re sure of, but a theory is something we’re tentative about. That’s not the difference between a law and a theory. The difference between a law and a theory is that a law would be a regularity that is known, and a theory would be something that explains the regularities…. So the reason evolution is called a theory is not because people are tentative about it, they’re certain it’s correct. It’s called a theory because it explains regularities. So the difference between a law and a theory is not the degree of certainty with respect to the thing in question, it has to do with the function it plays in science. A law is a regularity and a theory explains the regularity. So that would be why evolution is called a theory.
— J. P. Moreland, from Assessing the Crisis of Our Age Part 1 at 57:20