That may not even be what it's called .... I've heard at least 2 other terms for it on this board.
You put your top and backing right sides together and sew around 3 sides of the quilt (that's the pillowcase idea). Use the open side to turn it right side out. To finish - on the last (open) side iron 1/4 inch towards the inside. DO that to both backing and sides and either handstitch or machine stitch it closed.
I only leave about 1/3 of the last side open. Smaller area to turn it right side out through, but also smaller area to sew.