Draft orders can be created in Shopify to manually configure an order and send that order to a customer to allow them to check out.
They are listed in Orders > Drafts.
Why does ADU (Automatic Discounts & Upsells) use Draft orders?
Draft Orders allow for more flexible applications of discounts to products. They can also be programmatically created. This is why the Automatic Discount & Upsells app (as well as many other discount apps on Shopify) leverages Draft Orders.