Might be a terminological ambiguity -- like in mathematics you can distinguish "subsets", "proper subsets", and "nontrivial" (or "nonempty") subsets. Or "diviso

Might be a terminological ambiguity -- like in mathematics you can distinguish "subsets", "proper subsets", and "nontrivial" (or "nonempty") subsets. Or "divisors" and "nontrivial divisors" and "proper divisors". Even though the terminology can be defined in order to make these distinctions clear, there's an arbitrariness in terms of which definition you prefer (in the past, some mathematicians treated 1 as prime, which makes the definition of a prime simpler, but makes many theorems about primes more complicated to express). And there's a likelihood that even experts will sometimes use the simple term informally when they technically mean a more specific thing (like occasionally saying "divisors" instead of "proper divisors", or something). I imagine that acoustics experts have a definition available that definitively states whether the fundamental "is" a harmonic, but in certain contexts it intuitively makes sense either to include or exclude it, regardless of that. A similar case might be "animals"; taxonomically humans are animals (and apes), which is very important sometimes and confusing other times.