An operational definition specifies how a variable is measured or manipulated in a particular investigation. Defining stopping performance by a specified stop-signal task, scoring rule and estimation procedure makes the observation reproducible enough to inspect. The broader psychological construct of response inhibition need not be identical to that one procedure.[ref]
APA Dictionary of Psychology by the American Psychological Association. Operational definition entry: definition through specified operations or measurement procedures
For example, “number of correctly named digits from 1 to 10 under these instructions” operationally defines a numeral identification score. It leaves open whether the same child can compare quantities or count objects. An operational definition makes the measurement concrete; evidence about what that measurement represents is a separate question of construct validity.
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An operational definition is a clear, precise explanation of a concept or variable that specifies how it will be measured or manipulated in a particular study or experiment. It translates abstract concepts into measurable and observable terms, allowing researchers to assess and quantify them in a consistent manner. For example, if a researcher is studying "stress," an operational definition might specify that stress is measured by the number of self-reported stressful events in the past month or by physiological measures such as cortisol levels.