Under the law, many aspects of a musical composition can be copyrighted, including melody, lyrics, rhythm, and chord progression, so long as the creation reflects a 'minimal spark' of creativity and originality. That 2015 verdict is currently on appeal.
The most famous recent example, of course, involves the $5.3 million jury award to the family of Marvin Gaye over the hit song “Blurred Lines” by Pharrell Williams and Robin Thicke. The Music Copyright Infringement Resource tracks the earliest case to 'The Cot Beneath the Hill' trial in the Southern District of New York in 1844. 'Music plagiarism' has become a buzz phrase in intellectual property circles in recent years, particularly as digital music sampling has become exceedingly common. The term is now interchangeable with 'music copyright infringement,' though such claims are nothing new to the recording industry.