Pay-per-click (often known as PPC) describes any visit to your website for which you have paid. For example, the sponsored listings at the top and to the right of Google pages are PPC advertisements; so too are some of the banner adverts that you see on sites like price comparison websites.
On search engines, PPC marketing generally involves an advertiser (that is, your business) ‘bidding’ on a click. You set the price you wish to pay for each click, and you will then compete against other advertisers that are bidding on the same keywords. This bidding process is completely automated, and happens virtually instantly.
Sometimes advertisers will be charged a flat rate for each click. This practice is particularly common on price comparison sites.