Order Batching: When 2 or more customer shopping carts are merged into one order
In the Fast Checkout customer experience, users have 5 minutes to make changes to their order. During the time window, they are able to update items in the cart, cancel order, and other checkout related interactions. If the user closes the window and purchases another item on the same store during the 5 minute timer, their new purchase will be "batched" with the previous one.
Fast piggybacks the new item into the user's active order. Most of this is handled invisibly to the seller. What it will look like in the server API calls is when an order is batched with a new purchase, the original order will get an update call with a new item.