What does the acronym PO stand for in retail?

This may be one that is country specific as it not normally one seen - however the ones you would see are

POP Point of Purchase - Typically refers to all materials and physical setup in a retailer, in and around where the product is displayed

POS Point of Sale - Typically refers to materials, brochures, signs at point of sale, or can refer to point of sale cash register

POSA Point of Sale Activation - Process by which software becomes activated, useable, at the point of purchase

POV Point of View