DA Stands for dual action. A DA Sander will move to 2 ways. Firstly the pad.disc will rotate in a circular motion, as you would expect. However to replace the motion of hand sanding, ie if you are using sanding down using your hand and sand paper you would not just move the paper perfectly round and round. Therefore the second motion of a DA Sander is an orbital motion that moves the circular motion over a bigger area. The mini orbital sander from cp is a dual action sander