A case study is sustained, detailed examination of a single instance — one organisation, one patient, one policy, one event — on the assumption that the particular repays close attention. Beyond that the term splinters. Some traditions treat it as a research design with a logic of its own, capable of supporting inference; others treat it as an illustrative form that sets up questions rather than answering them; business schools and law schools use “case study” for a teaching document that is not research at all. No body adjudicates between these uses, and the methods literature that discusses them argues rather than rules. The common core is stated here and the divergence is named, because presenting one author’s definition would make a contested position look like doctrine.
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.
Deeper treatment: this term also has a full entry in the Business Library.