Why do we refer to pressure unequilibrium as partial vaccuum?

Question

I was reading about Newcomen’s engine where the introduction of water to the cylinder makes the steam go into liquid, and they refer to it as “partial vaccuum” creation. How come?

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Answer 1

A partial vacuum is a pressure differential by definition. I think you’re asking specifically about the nomenclature for which I’m not an expert. However, the word vacuum comes from the Greek word “vacuus” which means void. In a perfect vacuum, there is no matter I.e. it is totally “void”. In a partial vacuum, matter exists. Hope this helps.