What is the difference between purchase order and sales order?

Purchase order opposite Sales Order .Purchase Order issue from : management of procurement and reqired from production department .Selling Orede issued by: Marketing Division  and  required by the customer.In actions:Purchase Order needs to request materials sales Order needed to support the delivery .

Purchase orders are for buying or aquiring things while sales order is for selling or disposing.  

Sales Order being received from third party, Purchase order is being issued to third party

Sales Order is issued when a customer buys something from your company while the Purchase Order is issued when the company buys something from the vendor.