What is a word describing words like stuff and thing?
Solution 1:
Not sure if I'm encompassing the concern about using a definite article the for a term, but they could be referred to in general as vague, non-specific, or generic terms.
Vague: Thinking or communicating in an unfocused or imprecise way.
Non-specific: Not detailed or exact; general.
Generic: Characteristic of or relating to a class or group of things; not specific.