the·o·ry noun \ˈthē-ə-rē, ˈthir-ē\
: an idea or set of ideas that is intended to explain facts or events
: an idea that is suggested or presented as possibly true but that is not known or proven to be true
: the general principles or ideas that relate to a particular subject
A scientific theory summarizes a hypothesis or group of hypotheses that have been supported with repeated testing. If enough evidence accumulates to support a hypothesis, it moves to the next step—known as a theory—in the scientific method and becomes accepted as a valid explanation of a phenomenon.
As used in science, however, a theory is an explanation or model based on observation, experimentation, and reasoning, especially one that has been tested and confirmed as a general principle helping to explain and predict natural phenomena.
Before you chastise him for not using the correct word, can you give me some evidence where they have observed evolution? Hint the have been testing millions of generations of flies for over 70 years now...