Well, the name of the second largest country in North America is "[The] United States of America", commonly abbreviated to a smaller mouthful as "the USA" or "the US" or "America".

Now if only the founding rebels had actually given the place a name, rather than a description of what/where it is, the darned place would be easier to discuss!

There are other "US" countries, and other countries in the Americas.

No worries, we all know what's usually meant by America.

Cheers