Definition
Operationalization
Translating an abstract concept into something concrete you can measure — defining exactly what counts as "stress", "engagement", or "success" in your study.
Research questions are about constructs; data collection needs operations. Operationalizing "student engagement" might mean attendance plus a validated questionnaire plus time-on-task logs — each a defensible, partial window on the construct. The choice shapes everything downstream, including what your findings can claim.
Good practice: use established operationalizations where they exist (comparability across studies is worth more than novelty), state yours explicitly in the methods, and acknowledge the gap between measure and construct rather than quietly equating them.