Final answer:
The term that describes the results of repeated observation in the form of a mathematical expression that characterizes a natural phenomenon is a scientific law.
Step-by-step explanation:
The results of repeated observations that are typically described as a mathematical expression and elucidate a natural phenomenon are known as a scientific law. The correct answer to the question is therefore C. Law. Scientific laws summarize vast numbers of experimental observations and can often predict some facet of the natural world. A law is the final step in the scientific method, following observation, hypothesis formulation, and theory development, once the hypothesis has been extensively tested and verified. A scientific theory is a well-substantiated explanation of an aspect of the natural world that can be modified with new evidence. In contrast, a hypothesis is a tentative explanation, which, when supported by substantial evidence, can rise to the level of a theory.