How would you best describe a scientific theory

A scientific theory is a suggested description that explains
the cause or nature of things that have been observed. 

The theory usually also predicts things that have not been
observed yet.  Then, experiments are set up to test the predictions. 

If the experiments come out as the theory predicted, that result
supports the value of the theory, and brings it closer to being accepted. 

If the experiments don't come out as the theory predicted, then the
theory is either tweaked or rejected completely.