I'm sure I could think of more. But in addition to these multiple definitions,

How about the definition where the unemployment rate for these workers is below the natural unemployment rate?

Finally, there is the question of domain size. Who is a STEM worker? Are we just talking about software engineers in Silicon Valley? Are we talking about anyone who majored in a STEM field? Are we talking about anyone who works with a computer on a daily basis?

This one is pretty easy. For the purposes of this debate, it would be the main profession of the foreign workers that are being brought in to fill the perceived shortage. Or if you flip it around, it is the main profession of workers that would be leaving for foreign countries if the industry stagnated or collapsed and we started experiencing a "brain drain". Engineers.

Supporters of high-skilled immigration (including Yours Truly!) see the denial of "STEM shortages" as the beginning of an attempt to restrict high-skilled immigration in order to boost the incomes of the upper middle class.

This is supposing that one of the few remaining ways for upward mobility that's sustaining the American middle class is a bad thing. And it's basically shifting the goal posts of what it means to be a member of the middle class. In terms of having the disposable incomes to buy homes, cars, start families, pay for their children's college, this group of people aren't that much better off than a factory worker from the 1960's, while the rest of the middle class is getting screwed pretty good.

Ironically, I am an immigrant in the tech field (I immigrated 30 years ago as a child and also served int he US military). But if this country fails to continue cultivating a strong, home-grown engineering labor force to stay ahead of foreign markets, and instead uses immigrant labor to depress middle-class wages, I will happily move to a different country that offers me a higher standard of living, better working conditions, and comparable pay.