What is C Corporation?

Legal Definition
A C corporation, under United States federal income tax law, refers to any corporation that is taxed separately from its owners. A C corporation is distinguished from an S corporation, which generally is not taxed separately. Most major companies (and many smaller companies) are treated as C corporations for U.S. federal income tax purposes.
-- Wikipedia
Legal Definition
Any corporation that does not qualify and elect to be an S corporation under the Internal Revenue Code. Unlike S corporations, C corporations must always pay income taxes directly to the federal government.

See 26 U.S.C. § 11 and 26 U.S.C. § 1361(a)(2).
Legal Definition
A corporation in the United States that, for Federal income tax purposes, is taxed under and Subchapter C ( et seq.) of Chapter 1 of the Internal Revenue Code.A C corporation may also be subject to a separate Federal income tax called the Alternative Minimum Tax.