This is a compilation of choruses on famous utattemita songs.
A chorus or gasshou is a fan-made chorus in which covers of various utaite are mixed together. The utaite themselves are usually not involved in the process of creating such mixes. Gasshou is related to awasetemita.
The term "chorus" in the meaning of gasshou is not to be confused with the meaning of YouTube choruses, which are generally just mass collaborations.