Answer:
A well tested explanation of a natural phenomenon
Step-by-step explanation:
A scientific theory is an explanation of a natural phenomenon which has been drawn from a well tested observation.
Theories are products of repeated scientific experiments. When a hypothesis otherwise known as a "scientific guess" survives a lot of scrutiny, we can elevate it to the status of a theory. Most theories starts off from simple observations. These observations can further spark series of experiments in such a field and a scientific guess proposed. Further testing and experimenting would now lead to a theory.