Theme is the underlying thought of an article or discourse. In the law of copyright, the underlying thought presented in an original way, characterized by novelty or embellishment, so that it becomes the literary property of the author in the exclusive use of which s/he is entitled to protection.
It is the theme presented in an original way with novelty of treatment or embellishment which becomes the property of an author, in the exclusive use of which a copyright will protect him. [Roe-Lawton v. Hal E. Roach Studios, 18 F.2d 126 (D. Cal. 1927)]