FIFO stands for first-in, first-out, meaning that the oldest inventory items are recorded as sold first. In other words, the cost associated with the inventory that was purchased first is the cost expensed first.
Customer orders will be linked to as early supplier (incoming) orders as possible (based on the order supplier ETA) (limited to the start and end date of the delivery window)
LIFO stands for last-in, first-out, meaning that the most recently produced items are recorded as sold first.
Customer orders linked to as late incoming supplier orders as possible (based on the order supplier ETA) (limited to the end date of the delivery window)
LIFO is good if you have two delivery windows that share products and the date of its date span, then no customers ordering in the late delivery window book goods for those who order in early delivery window.
FIFO / LIFO plays only the role of the delivery window with products that have "link" or "stock/link". "Preorder" for example will never try to allocate the stock or supplier orders while "stock" only attempts to allocate the store warehouse.