Concepts and Operations
Concepts used in research are defined operationally. That is, they are defined as the operations used to measure them.
For example, intelligence is often defined in research as a score on an intelligence test. To measure intelligence you perform the operations of administering and scoring an intelligence test.
Operational definitions make your terms clear and their limitations apparent. Intelligence is definitely a less resounding term when you realize it means nothing more than a score on the Wechsler Adult Intelligence Scale, say.
If you want to make your definition more robust, you can combine measures (administer two or three intelligence tests, for example). A single score for the combined measures can be calculated by standardizing and scaling, as long as the measures are correlated. If the measures turn out not to be correlated, you've learned something useful about the adequacy of your concept.