Is the USA a Democracy or a Republic, as a country?

"a Democracy" is just an abuse of language to designate a Bourgeois Republic with a high level of formal democracy (formal but not concrete: most of the important decisions are considered as part of an inviolable "economic sphere" on which the people has no right of collective decision).

Other forms of republics have existed in History, including versions based on aristocracy and with little power attached to capital, so the term Republic alone would be quite vague.

But Democracy doesn't really make reference to a well-defined concrete political system. Democracy is an abstract concept, like Liberty or Justice.

Both. A republic simply means "not a monarchy". And the USA has elections where there is a free choice, so it is a democracy. If you can't see that it's a democratic republic, you aren't using the words properly.

definitely, no doubt a plutocracy

its both