A scientific theory is a well-substantiated explanation of some aspect of the natural world, based on a body of evidence. It is developed through the scientific method, which involves observation, experimentation, and analysis. Unlike a hypothesis, which is a testable prediction, a theory has been repeatedly tested and confirmed through various experiments and observations. Scientific theories can evolve over time as new evidence emerges. For example, the theory of evolution explains how species change over time through natural selection. Other well-known theories include the theory of relativity in physics and the germ theory of disease in medicine, both of which have significantly advanced our understanding of their respective fields.