Originally Posted by Sadiemae

Let's see if I can explain so that this makes sense.
They are called Stack and Whack because you cut a fabric into sections WOF of identical repeats of the fabric. Then you layer or stack these sections so that when you stick a pin in a certain spot down through all of the layers your pin will poke each fabric in the exact same place (or as close as possible). Usually you use flower pins or pins that lay completely flat without a ball on the end. Once you have these layers or stack of fabrics pinned, you whack which means to take your rotary cutter and ruler and cut your pieces for the quilt. In doing this your triangles or whatever shape you are using will make a star or block in which all of the pieces are identical.
The Book is Stack and Whack. If you search Stack And Whack you will get many threads on them.