A chorale is the melody of a Christian hymn, or religious song. You're most likely to hear a chorale in a church.
You can use the noun chorale to talk about a church song, or more specifically, the tune which the voices sing. Most chorales are sung in harmony, blending higher and lower voices, and are fairly simple melodies that are relatively easy to sing along with. The word comes from the German Choralgesang, "choral song," with its Latin root of cantus choralis, "song belonging to a choir."