What does the term 'operationally defined' refer to in research?

The term 'operationally defined' in research refers specifically to how a concept is measured or quantified within the scope of a study. This involves creating specific criteria or procedures that allow researchers to systematically observe, measure, and evaluate the concepts they are investigating. For instance, if a researcher is studying 'stress,' they must operationally define it in a way that could involve measuring physiological indicators, self-reported questionnaires, or behavioral observations. This clarity is essential because it ensures that the concepts being studied can be consistently understood and evaluated by others, thereby enhancing the reliability and validity of the research findings.