A difficult-to-determine number, waste refers to the point at which it's no longer economically sound for a marketer to continue targeting a message at you. For example, if an advertiser is looking for direct response and you've seen or heard their ad 40 times without buying, they might want to consider spending their money on a different customer. Waste can also refer to extravagant media expenditures, like buying every ad on "Friends" for a month.