Search Engine Marketing applies to keyword-targeted ads shown on search results pages and on sites in the search network within a search engine. Ads shown on these pages appear alongside the search results and are specific to that particular search query. If the advertiser's keyword matches the user's search term, the advertiser's ad could appear.
When and only when the ad is clicked on, the advertiser will incur their bid amount of the click (CPC). If the same user clicks on the ad multiple times, the advertiser is only charged once, and the advertiser is not charged when ads are displayed but not clicked on (as opposed to placement targeted campaigns where you can pay by the impression).
