On the one hand, it can mean a coherent system of rules and principles, a more or less verified and established explanation accounting for known facts or phenomena. On the other hand, it can refer to speculation, a guess or conjecture, or an untested hypothesis, idea, or opinion. Such bodies of knowledge are called theories. We cannot emphasize too strongly that the word theory has a very different meaning in science than in everyday life. Facts are the world's data.
Theories are structures of ideas that explain and interpret facts.
Ain't So .