MCW stands for Mock Cathedral Window quilt. It is when you use circles and sew them together on the inside straight lines to form blocks. The circle edge or curve part is then folded over towards the center front to form scallops. The scallops can be the design itself or a square of fancy fabric can be put in the frame before the cuves are sewn down. There are some nice examples on Quiltingboard but also on the net. You might find them under MCW or circle quilts.