SEM - Search Engine Marketing. The objectives of SEM are to (1) attract visitors to your website and (2) have them "convert." A conversion is defined differently depending on your site's objectives. For example, if you are selling products through your website then you may define a conversion as a purchase. If you are a service-based company you may define conversion as the submission of a "contact us" form. SEM is broader than SEO, and may incorporate SEO into the overall marketing plan. SEM may include pay-per-click advertising. It reviews web traffic analytics and measures goals and conversions.