A number assigned to an order, commonly used in online shopping, restaurants, and customer service.
Please enter your order number to check the delivery status.
注文 means 'order' in general, while 注文番号 specifically refers to the identifying number of an order.
番号 is a generic 'number', whereas 注文番号 is a specific type of number used for orders.
Compound of 注文 (order) and 番号 (number).