stock.picking is a main object that is used for Internal Moves menu. stock.picking.in is an object, inherited from stock.picking that is used for Incoming Shipments. stock.picking.out is an object, inherited from stock.picking that is used for Delivery Orders.

Basically, These 3 menu refers the same object, some functionality makes them separated like type field which is differed in all objects. type = out means Delivery Orders, type = in means Incoming Shipments and type = internal means Internal Moves. Hope this will help you.

Thanks, Priyesh Solanki