A theory is called a theory because it's a well-substantiated explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses. Here's a breakdown:

1. It's not just a guess: A theory is not a wild speculation or an opinion. It's based on evidence and rigorous testing.

2. It's supported by evidence: Theories are supported by a large body of evidence that has been repeatedly verified through experiments, observations, and analysis.

3. It's explanatory: Theories provide a coherent explanation for a phenomenon, connecting different observations and facts into a unified framework.

4. It's predictive: Theories can be used to make predictions about future observations or experiments, which can then be tested to further validate the theory.

5. It's falsifiable: A true theory is open to being disproven. If new evidence emerges that contradicts the theory, it can be revised or replaced.

Examples:

* Theory of Gravity: This theory explains why objects fall to the ground and why planets orbit the sun. It's supported by countless observations and experiments.

* Theory of Evolution: This theory explains the diversity of life on Earth through natural selection. It's supported by fossil evidence, genetic studies, and observations of evolution in action.

Theories are constantly evolving: As new evidence emerges and our understanding of the world grows, theories can be refined, expanded, or even replaced. However, this doesn't mean they are "just theories" in the sense of being unreliable or untested. They are the best explanations we have based on the evidence available.