What do you mean by US-usA?

There are three definitions of the "United States" in Black's Law Dictionary; two are in common, statutory use . . .

"U.S."/"United States": The "U.S." may be most succinctly described as the Federal Area(s), and may generally be defined as the District of Columbia and its Territories. In the Internal Revenue Code (Title 26, U.S. Code), the term "United States" includes (meaning includes only), the "States" (meaning federal Territories), and the District of Columbia. Federal Areas are referred to as "domestic" — in contradistinction to "national".
Note 1: "States" (meaning Territories): The post "Civil" War Congress had the temerity to re-define 'the word "State" to mean and include a Territory and District of Columbia'; on the same day (See Note 4 below.) the so-called "14th Amendment" was expected to be ratified.) (!)

"u.s.A."/"united states of America": The "u.s.A." (usually capitalized as "U.S.A."), may be defined as the "collective name of the states which are united by and under the Constitution" for the United States of America.
Note 2: "collective name . . . Constitution": Hooven & Allison Co. v. Evatt, U.S. Ohio, 324 U.S. 652, 65 S.Ct. 870, 880, 89 L.Ed. 1252. — Black's Law Dictionary, Sixth Edition.
Note 3: Preamble "title"; there is NO title above "We the People"; the words Constitution for the United States of America conclude the 1st paragraph of the Document. The phrase "Constitution of", or "U.S. Constitution", are illegitimate; their parents/authors are either ignorant — or their motives are highly suspect . . .

The non-capitalized "united" is retained from President Jefferson's "The unanimous Declaration of the thirteen united States of America", of July 4, 1776. Who dares object? Moreover, the signatories (signers), were elected Representatives, making that "Declaration" an organic Document of this Nation's history.

Far less understood, however, is the unfortunate Reason for our refraining from capitalizing "States". At another place, we will explain what our Founder justly refers to as a 'Legislative coup d'etat of the U.S.A., by the federal "U.S."'!
Note 4: Statutes, U.S. Congress, Volume 15, Pg. 166; July 20, 1868. By that act — for which there was never any Constitutional authority — the powers delegated by the Constitution to Congress appeared expanded, as "exclusive Legislation" over Federal Areas ("U.S."; limited under Article I., Section 8, cl. 17), has since been wrongly believed to be applicable to the Nation ("u.s.A.").

Most relevant example: The Internal Revenue Code, at Section 3121 (e), in referring to the term "State", and the "United States", includes (meaning includes only), the Federal Areas of: (1) the District of Columbia, (2) the Commonwealth o="Texas">Texas         Postal Zone: [Constitution for the United States of America; that is: to restrain government from usurping from the People, their true role as the collective Sovereignty. This Web-Site is dedicated, to the Re-Constitution.