If you have a customer that will no longer be purchasing an Item, or a customer that will no longer be purchasing from you at all, on any sku (e.g. they have gone out of business), there are a few features you can use:
Lost Item-Customer - This is if the customer (including all associated customer ship-to's) has stopped buying a particular SKU, and you wish to remove that demand history such that purchasing behavior is reduced. See the Lost Item Customer topic.
Lost Customer Ship-To - This is if the customer-ship-to has stopped buying from you on ANY product. See the Lost Customer Ship-To topic.
Lost Item Customer Ship-To- This is if the customer-ship-to has stopped buying a particular SKU from you