In Magento 2, custom order numbers allow you to modify the default sequential numerical pattern used for generating order identifiers. By implementing a custom order number module or extension, you can define your own logic to create order numbers that align with your business requirements. With Magento 2 custom order number module, you have the flexibility to configure various options such as prefix, suffix, padding, and increment value. This allows you to customize the format and structure of your order numbers according to your preferences.