**Operational Definition** - description of term as applied to a specific situation to facilitate the collection of meaningful (standardized) data.
When collecting data it is important to define terms very clearly in order to assure all those collecting and analysing the data have the same understanding.
Therefore, operational definitions should be very precise and be written to avoid possible variation in interpretations.

The New Economics by W. Edwards Deming, page 105: "An operational definition is a procedure agreed upon for translation of a concept into measurement of some kind."

An operational definition specifically states how to measure the item being defined. Many difficulties can arise without operationally defined measures. For example, how would you decide whether your plane arrived on time? Landing by the time stated as the arrival time, stopping at the gate, the first passenger leaving the plane, the last passenger leaving the plane, the last passenger leaving the plane within 10 minutes of the printed arrival time? How would you measure the number of trees in a park: does it count as a tree if it appears to be dead, what if it is just a stump, what if it is just a 2 inch tall sprout, what if it seems like a tree but in classified as a bush by horticulturists. How would you count the number of attendees at a sporting event? The number of tickets sold (regardless of whether they actually are used), the number of people who use a ticket to get into the event, every person at the event (spectators, workers at the arena, vendors, athletes), number of spectators with tickets arriving before halftime?

Online Resources:- Operational Definition Handbook - 21 pages on operational definitions.
- Operational Definitions and Data Collection