What is "counter-melody"

In music, a counter-melody (often countermelody) is a sequence of notes, perceived as a melody, written to be played simultaneously with a more prominent lead melody: a secondary melody played in counterpoint with the primary melody. A counter-melody performs a subordinate role, and is typically heard in a texture consisting of a melody plus accompaniment.

In marches, the counter melody is often given to the trombones or horns (American composer David Wallis Reeves is credited with this innovation in 1876.) The more formal term countersubject applies to a secondary or subordinate melodic idea in a fugue. A countermelody differs from a barbershop quartet-style harmony part sung by a backup singer in that whereas the harmony part typically lacks its own independent musical line, a countermelody is a distinct melodic line.