It is literally Italian for "group", and is generally meant to be the set of drivetrain components that go together. Therefore, the Campa Record gruppo would include Ergolevers, front and rear derailleurs, crankset, brakes, bottom bracket, hubs, chain, etc.
But lately I have seen more and more gruppi listed by shops without hubs, which makes sense as any prebuilt wheels you buy will include hubs.
And other shops offer super-gruppi, which include seatpost, stem, etc. as a sales ploy and to make sure you have everything to build a bike.
Bottom line is to be sure you know the parts list before you buy lest you end up with fewer parts than you expect and/or need.
As for English, it is always a question of whether to use the native language word or your own. Pick one.
Cheers...Gary