This is the 6314th most frequent Japanese word.
コーラス
"Chorus" (singing group or refrain in music).
コーラス is used to refer to a group singing activity or choir here.
学校の音楽クラブでコーラスを練習しています。
We are practicing chorus in the school's music club.
コーラス refers to the specific sections in a song where group singing occurs.
この曲でコーラス部分を担当しました。
I was responsible for the chorus parts in this song.
コーラス in this sentence implies her singing contribution that creates harmony in the song.