A few seconds on the website search engine would answer everything
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To the uninitiated "output valve control grid capacitor" is going to be just as confusing as "that capacitor". If somebody is going to be too afraid to ask for clarification to an answer I doubt they would ever started a thread in the first place.
We also use other vintage terms for capacitors like "waxies" and "condensers" which, nowadays, could confuse the initiated and uninitiated alike, but I kind of like the idea we still use them and keep them alive
David