Chorus is a synonym for Choir.
Refrain is the part of a song which is repeated. Yes, Refrain "stop oneself from doing something" (unless oneself is singing a chorus, with or without accompanying choir, I guess).
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On first & second listen the long songs really appealed to me - the complete opposite to my MoS experience. Now after 6 to 8 listens, the shorter songs are starting to stick in my head. There is so much to love on AtWB, but I think my top picks are:
1: The Gift of Music
2: I Am
Other than that, it's still too soon to say.