Operational Definition:

A definition of a concept in terms of how the concept will be manipulated, measured, or observed.

Example: How do you study "hunger"?

•Can’t just ask people--may have different meanings for "hungry."

•Might want to study hunger in rats. How do you know when a rat is hungry?

You have to operationalize the definition of "hunger." You define hunger in terms of what you’ll manipulate or observe.

In this case, you may define "hunger" as the subject (human or rat) not eating in the past 12 hour period.