Search Engine Marketing, or SEM, is a form of Internet Marketing that seeks to promote websites to search engine users by increasing the website’s profile so that it will appear as high as possible in the results list (also referred to as the Search Engine result pages (SERPs).

SEM methods include: Search Engine Optimization (or SEO)
paid placement (or PPC)
paid inclusion (you have to pay to get into the search engine)
allowing search engines full access to your content for free as a way of enticing buyers