Invalid traffic, also known as ad fraud, is a term used in the online advertising industry to refer to traffic or impressions that are generated by means that are fraudulent or not in accordance with industry standards. Invalid traffic can take many forms, such as fake impressions, bot traffic, or click farms, and can have a negative impact on both advertisers and publishers. Invalid traffic can waste advertisers' budgets, as they may pay for ad impressions that are not seen by real users. It can also harm publishers, as it can reduce the value of their inventory, and can damage their reputation and trust with advertisers. Invalid traffic is a major problem in the online advertising industry, and is estimated to cost advertisers billions of dollars each year.