To translate an abstract concept into a specific, observable, measurable procedure; every operational definition embeds theoretical choices about what the concept means and what it excludes.
To operationalise a concept is to specify the observable procedure by which it will be measured or identified in a study — turning “trust”, “poverty” or “engagement” into something a particular instrument records. The operational definition is a decision by the researcher, and rival operationalisations of the same concept regularly disagree with each other, which is why findings about a construct can fail to line up across studies. The term arose in debates about measurement in the empirical sciences and carries a residue of those debates: some treat operationalisation as a working necessity, others have warned against mistaking the measure for the concept. That criticism is substantive and is flagged here rather than concealed.
Why this entry carries no source list. This lexicon cites an official primary source wherever one exists, and says so plainly where none does. No body governs this term. There is no standards organisation for it, no register, and no text whose authors could claim to have settled its meaning. Methods literature describes practice and argues about it; a citation to one author would dress a position in a live argument as a rule, which would mislead more than silence does. What follows is the convention as it is actually used, with the disagreements named rather than smoothed over.