In pay-per-click advertising, negative keywords stop search ads from appearing in search results for ads containing those negative keywords. If your product is often confused with another industry, you can use a negative keyword for the other industry, which would keep your ad from showing.

For example, a local hair salon, “Custom Cuts,” is often confused with the local lawn care business, “Custom Lawn Cuts.” If you were running Google ads, they may show your ad (and you would pay money) when someone was meaning to search for lawn care. Including the negative keywords would prevent you from wasting money.