I noticed some songs having this effect1, almost always rock/pop ones: A singer just finishes singing a verse, and meanwhile a (the same or another one) singer starts singing another one.
This effect is especially visible in this song: Bon Jovi - This house is not on sale, for example at this point (between the boldened verses):
Where memories live and the dream don't fail.
This house is not for sale.
What is this effect1 called?
1: I'm calling it an 'effect' because I don't know how else to call it. Feel free to edit.