Search engine marketing or SEM is a form of marketing, where the channel to deliver the marketing message is the search engine.
The Search Engine Marketing (SEM) definition is a seriously different from the different sources. The Wikipedia itself is failing here, and not hiding it. Here is their definition of Search Engine Marketing:
Search engine marketing, or SEM, is a form of Internet marketing that seeks to promote websites by increasing their visibility in the ‘Inorganic’ search engine result pages (SERPs). According to the Search Engine Marketing Professionals Organization, SEM methods include: search engine optimization (or SEO), paid placement, and paid inclusion. Other sources, including the New York Times, define SEM as the practice of buying paid search listings with the goal of obtaining better free search listings.
Did you get it? Do you know what is SEM now? No? Neither do we!
The problem is the word ‘Marketing’ and it’s incompatibility with the search engine optimisation, that is a purely technical and statistical task. Marketing is in its nature ‘creative’, and SEO is the statistical analysis applied in practice.
Search engine marketing is a form of marketing, where the channel to deliver the marketing message is the search engine.
Google is the most used search engine and it has its Google AdWords product that enables a marketer to spend the search engine marketing budget. Yahoo and MSN and trying to compete, but the gap between them and Google is actually widening constantly. That actually means that the search engine marketing is paying Google AdWords to show a link to your site in the right hand side column, next to the real (organic) results.