I'll just give you one, and it is highly relevant. You hear creationists say "Evolution is only a theory". That is the street usage of "theory", used as a synonym for "opinion" or "guess"; one can almost hear the implied sneer "merely" in their barely concealed hisses. A theory in science is a coherent body of knowledge sustained by constant testing in and outside of laboratories, the purpose of which is to reject hypotheses shown to be wrong by such tests. These results are then used to modify the theory so as to accord better with observations. Karl Popper proposed his eponymous Popper criterion for a theory to be scientific -- it must be falsifiable, i.e., there must be tests that can expose wrong predictions of the theory. See the link below. In this strict sense, no scientific theory is ever absolutely correct, not even quantum physics, for who knows what future experiments may wrought? However, something like Newtonian mechanics (a classical approximation) is the basis of bridge and skyscraper designs because it is a good enough theory for ordinary sized objects. Scientific theories are marked by their inherent modesty -- scientists will be the first to admit that their theories cannot explain everything. Indeed, a "theory" that explains everything explains nothing.