ProductUpdate date is to keep track of the last time the product was updated so that stock can be adjusted based on the inventory at that time.
Stock is the number of items in stock at the last update date.
Product live is a true false field that allows you to quickly add or remove a product or stage it on the back end before making it live for users to purchase.
Product unlimited is a true false boolean field that can be used to mark an item exempt from inventory concerns so that it will be available in stock regardless of inventory.