An experimenter is interested in studying the relationship between hunger and aggression. She decides that she will measure aggression by counting the number of times a participant hits a punching bag. In this case, her definition of aggression is the number of times the participant hits the bag.

Explanation:

The operational definition is the description of a specific process, or set of validation tests, accessible to more persons than the definer (i.e., said to be publicly accessible), where it can be repeatedly measured or tested

Operational definitions are also used to define system states or (nonspecific) physical objects by the description of a specific process of preparation which can be repeated

For example in the given example experimenter is using the case of hitting a punching bag to measure the level of aggression in someone