A determiner (a cover term) is an °article or an °adnominal °demonstrative.
The term was introduced by Bloomfield (1933) as a cover term for articles and demonstratives in English, because these occur in the same slot and are mutually exclusive. But they also have some semantic similarity, so the term can also be used as a comparative concept, for adnominal modifiers that are articles or demonstratives.
determiner (CXN) = a superordinate category of contextually defined forms that combine with common nouns; determiners include both demonstrative attributives and articles. (Section 3.2)