What is waste? It is one of those words we use with remarkable confidence and very little reflection. We waste food, time, opportunities, money, talent and, on particularly difficult days, even our lives. The meaning seems so obvious that the question itself almost feels unnecessary. Yet the more I thought about it, the less obvious it became. "Waste" seems like a simple word, but it depends entirely on what standard you judge it by. Here are a few ways to think about it. Physics: Waste does not really exist. Matter and energy are transformed, not destroyed. What is waste to one process becomes a resource for another. Biology: Waste is a byproduct that an organism cannot use and must expel. Economics: Waste is a resource that has lower value than it could have had. Throwing away edible food is waste because its potential value is lost. Engineering: Waste is inefficiency—energy, material, or time that does not contribute to the desired output. Human life: We usua...