Negative keywords are words or phrases you add to your ad campaign to stop your ads from showing on searches that are not relevant to your product or service. When a user searches using a term that matches a negative keyword, the ad will not appear, so you avoid paying for clicks that are unlikely to lead to sales. This process helps control your advertising costs by reducing wasted spending. For example, if you sell shoes but don't want to show ads for 'cheap shoes' or 'free shoes', you add 'cheap' and 'free' as negative keywords. When someone searches 'cheap boots', your ad won't show, saving money. Ads still show for relevant searches like 'boots for hiking'. This way, negative keywords help you focus your budget on the right audience and improve your campaign's efficiency.