What is Public Use?

Legal Definition
Public use is a legal requirement under the takings clause ("nor shall private property be taken for public use without just compensation") of the Fifth Amendment of the U.S. Constitution, that owners of property seized by eminent domain for "public use" be paid "just compensation".

The distinction between public use and public purpose has created a doctrinally confusing and highly controversial subset of public use doctrine. This controversy was renewed after the Supreme Court's decision. In Kelo v. City of New London (2005) the Court permitted for the first time, in a 5-4 decision, the taking of private property to and transferring it to a private developer for one dollar per year. In United States v. Gettysburg Electric Ry. Co., 160 U.S. 668 (1896), the US Supreme Court ruled in 1896 that seizing the railway for Gettysburg Battlefield historic preservation "seems" to be "a public use".

Takings that are not "for public use" are not directly covered by the doctrine, however such a taking will likely violate due process rights under the Fourteenth amendment, or other applicable law.
-- Wikipedia
Legal Definition
The availabilty of an invention for use by the public. An application for a patent can be done unless the invention has been in use for more than a year. If it has been in use for more than one year the application for patent can be denied.
Legal Definition
in constitutional provisions restricting the exercise of the right to take private property in virtue of eminent domain, means a use concerning the whole community as distinguished from particular individuals. But each and every member of society need not be equally interested m such use, or be personally and directly affected by it; if the object is to satisfy a great public want or exigency, that is sufficient. Gilmer v. Lime Point, 18 Cal. 229; Budd v. New York, 143 U. S. 517, 12 Sup. Ct 468, 36 L. Ed. 247.
-- Black's Law Dictionary
Legal Definition
Public benefit. See 2 S. & P. (Ala.) 199, 23 Am. Dec. 307; 1 Sax. Ch, (N. J.) 694, 23 Am. Dec. 756.
-- Ballentine's Law Dictionary