Final answer:
An operational definition sets specific, measurable criteria for studying a concept, like using the number of pushes or hits by a child to define aggression.
Step-by-step explanation:
Defining aggression as the number of times one child pushes or hits other children in a 5-minute period is an example of an operational definition. An operational definition is used in research to refer to a clear and precise description or measure of a concept so that the concept can be studied empirically and quantitatively. This approach sets specific criteria for observation and measurement, ensuring consistency and replicability in a study. For instance, while studying the concepts of childhood obesity or bullying, operational definitions would provide objective and quantifiable criteria for identifying when a child is considered obese or what behaviors constitute bullying.