countermelody
A secondary melody played simultaneously with the main melody.
In Depth
A countermelody is a subordinate melodic line that sounds alongside the primary melody, adding depth and interest to the musical texture. Unlike counterpoint, where voices are of equal importance, a countermelody clearly supports and decorates the main tune.
Countermelodies appear throughout music. In orchestral writing, a woodwind might play a countermelody while the strings carry the main theme. In pop music, a guitar riff or backing vocal line can serve as a countermelody. The Stars and Stripes Forever by Sousa features one of the most famous countermelodies — the piccolo part in the final strain.
Sousa's Stars and Stripes Forever has a piccolo countermelody so brilliant that it often overshadows the main march tune — audiences cheer when it enters.