Make to Order (MTO), Build to Order (BTO), and Assemble to Order (ATO) describe slight variations on the same manufacturing concept – make a product after receiving a confirmed order. This is in contrast to the make-to-stock concept, in which production is scheduled to achieve target stock levels.
MTO/BTO/ATO is more common for products which are customized, but may also be important to reduce waste or handle fluctuating demand. In general, customer lead times are higher for MTO/BTO/ATO compared to make to stock.