What is the difference between POS and POP materials?

By Definition: POP: Point of Purchase

POS: Point of Sale Point of Purchase would normally refer to that section in a store etc which stocks products for that particular category say, oral care, Skin Care and where the consumer/shopper actually makes her buying decision.

POPs are an aid to bring your product into the consideration set of the consumer/shopper. POS are normally available at the checkout counters, etc where the final sale is happening, where the consumer/shopper is actually paying for her purchases. It acts as a reminder to her that she might have forgotten X product. While POS trigger more impulse purchases than POPs but POPs aid the consumer/shopper in making an informed choice. The above said, often the two terms are used interchangebly owing to the bare minimum difference between the two.