Onion Powder is dried onion that is ground to a powder, to be used as a spice. It can provide an onion flavour in food where you wouldn't necessarily want chunks of onion. It is also useful in dry rubs, in breads, in DIY dry mixes, in flavouring soups, sauces and gravies at the last minute, etc. It is a "real" ingredient; not artificial. Just onion that has been dried, and ground.