For example, the first listing for noun, articular in Wallace's index points to pp. 42–46 (How to Distinguish Subject from Predicate Nominative), where the second principle is "The subject will be articular" (p. 43), with a number of examples (e.g., John 4:24: πνεῦμα ὁ θεός/God is spirit). From the perspective of someone who knows what articular means, itseems reasonable to expect someone who doesn't know its meaning to infer it. (See also the use of anarthrous in Wallace's discussion of "Colwell's rule" [pp. 5–6], which uses the term articulated without reference to the Greek article.)
So it seems to me that, perhaps, the lack of a definition of articular in at least some Greek grammars is a lacuna (small though it may be) in the field. For other beginning Greek students, an articular substantive is a noun, adjective, participle, etc. that is modified by an article, which will be in the same case, number, and gender. A substantive that lacks the article is called anarthrous.
But I would invite comments along one of two lines. First, if you know of an explicit (and perhaps more precise) definition of articular and/or anarthrous in a contemporary grammar (preferrably a beginning or intermediate grammar), please let me know. [disclaimer: I haven't done any research on this.] Second, if you're aware of any other lacunae within the literature, please give them here. Technical terms perform valuable functions in academic discourse, but when those of us who practice a certain discipline don't define those terms to help novices recognize and participate in our discourse, we become jargonistic and, even, provincial.