A paradigm is an outstandingly clear or typical example of something and, in its more consequential sense, the framework of assumptions and methods within which a discipline formulates its theories, laws, and experiments.
The plain sense is model or exemplar — a paradigm case is the instance you hold up to explain the rest. Grammar preserves a narrower version: the paradigm of a verb is the complete table of its inflected forms. The philosophical sense is the one that carries the weight, and it is largely Thomas Kuhn's doing. The Structure of Scientific Revolutions (1962) used the word for the shared body of assumptions, instruments, and exemplary problems that define normal science within a field. In Kuhn's account a paradigm is not amended when evidence contradicts it; anomalies accumulate until the whole apparatus is replaced at once — a paradigm shift. The phrase was borrowed so widely and so loosely that it now serves in business speech for any change of approach, a usage far weaker than Kuhn's.
The word arrived in English in the late fifteenth century from Late Latin paradigma, "pattern, example," from Greek paradeigma, from paradeiknynai, literally "to show side by side" — para- ("beside") and deiknynai ("to show"). The original image is something held up next to the thing being explained.
A paradigm is not an 📝archetype, which is an original pattern recurring across instances; the paradigm is the frame through which instances are viewed. Nor is it an 📝axiom, a single proposition assumed true — a paradigm is the entire apparatus, most of it never stated. It differs from an 📝ideology in kind: an ideology prescribes what ought to be, while a paradigm governs what counts as a question worth asking.