Search engine marketing (SEM) is a type of Internet marketing that commonly involves website promotion via increased visibility in the results pages of a search engine. This is most commonly done by using paid advertising. SEM will often include search engine optimization (SEO) which focuses on optimizing a site's content, code, and architecture in order to achieve increased page ranking.
Much of SEM focuses on buying ads that will appear on a search engine's results page—Google, Bing, and Yahoo are the current top search engines. These engines offer channels for businesses to purchase ads that will usually be display above the organic results. Usually, the higher the cost offered to pay for an ad will result in higher placement of said ad, though other factors may be involved such as the level of competition to appear on a particular results page. More often than not the paid advertising conducted in SEM is on a pay-per-click basis (PPC) where the customer is charge for each click on their ad.