A theory is a well-substantiated explanation of some aspect of the natural world, based on a body of evidence. Theories are developed through the scientific method, which involves observation, experimentation, and analysis. They help us understand complex phenomena and make predictions about future events. In science, a theory is different from a hypothesis, which is a testable prediction. For example, the theory of evolution explains how species change over time through natural selection. Similarly, the theory of relativity describes the relationship between space, time, and gravity, fundamentally changing our understanding of physics.