It refers to the advertisement model that is available on the internet where the payment is solely based on click-throughs.

As per an agreement in pay-per-click program, the advertiser is supposed to pay for only those clicks that are targeted towards a particular site and by using a definitive click-rate method. There exist different advertising options within PPC programs. Few such options include search engines, advertising networks, affiliate programs and so on. PPC can often be seen as a program that is in between paying per action and paying per impression. While PPC is seen in the light of paying per action, the publisher has to accept the risk that might be associated with offers that are less converting ones. While seen in light of paying per impression, the risk might have to be faced by the advertiser.