noun
song parody; new lyrics to an existing melody
Refers to taking a well-known song and replacing the lyrics with humorous or different words while keeping the original tune.
彼は有名な曲の替え歌を作って、友達を笑わせた。
He made a parody of a famous song and made his friends laugh.
この番組では、視聴者から送られた替え歌を
On this show, we introduce song parodies sent in by viewers.
Compound of 替え (change, substitute) and 歌 (song). The exact historical origin is uncertain, but the word naturally describes the act of changing lyrics while keeping the melody.