US = United States USA and U.S.A. = United States of America America is the continent.

Most Americans (U.S. citizens) mean the U.S. when they say 'America'. But that's not correct. As jdavp and luisfeliperasmuss wrote 'America' ist the continent. 'The Americas' or 'Both Americas' definetly would be 'Nort and South America' (counting as one or two continents). Here in Germany also most people think of the USA when they say 'America'. In Mexico, Brazil or Canada they may use this term (America) the correct (/proper) geographical way.

domasla, you forgot the Central America that includes Costa Rica, Honduras, Panama, and others.

U.S., U.S.A, USA 是美国 AMERICA 是美洲