Here is a great blog post about it http://gurneyjourney.blogspot.com/20...ney+Journey%29
I'll be with you in the squeezing of a lemon. ('_')
www dot marking paper dot blogspot dot com
I am going to throw out a somewhat different definition which may or not apply in the author's context. Massing can also refer to overlapping shapes to get one visual element. If twelve brown cows are standing together they create one mass instead of twelve smaller elements.