Any advertising where the cost is assessed based on the number of clicks. Most commonly, PPC refers to premium direct-placed fixed advertising on search engines. It is not exclusive to search, however, and can be found in many digital advertising products.
Compared to Search Engine Optimization (SEO), PPC is immediate. Ads will start delivering almost instantly once a campaign is setup. PPC offers guaranteed first-page placement on search engines (although they can appear on other pages, but only when an additional page is being viewed). PPC is more customizable and controllable than SEO, and can offer most precise conversion tracking. Additionally, PPC offers click-to-call abilities, where SEO doesn’t.
With PPC, the cost-per-click (CPC) varies based on several factors, mostly influenced by supply and demand and competition.