It gives a meaning to the concept or construct under investigation. It should distinguish it from all other concepts or constructs.

It defines an object, event, variable, concept, or construct in terms of the specific processes, tests, and measurements used to determine its presence or quantity.

Oxygen is a chalcogen that is a strong oxidizing agent and has the second-highest electronegativity of all reactive elements

Academic performance refers to the student's score in the finals.

Influenza is an acute highly contagious infection of the respiratory tract, which occurs sporadically or in epidemics and lasts up to a month.