1.NounA showing of something — such as a variable, term, or object — in terms of the specific process or set of validation tests used to determine its presence and quantity."The operational definition of a well-behaved student might be set at the threshold of "no more than 2 detentions in each semester".; To divide the spectrum of spicy sauces into three categories of "mildly spicy", "moderately spicy", and "extremely spicy", we set the operational definitions of "mild", "moderate", and "extreme" as (a) 0 to 3 × 10³ Scoville units, (b) more than 3 × 10³ up to 100 × 10³, and (c) more than 100 × 10³, respectively."