Search engine marketing
SEO - "Search Engine Optimization". The goal of all known search engines to find the user that he is looking for, and of course to make it more accurately and efficiently. On the Internet there are many sites. Search engines give a user's query sites in order of relevance, ie those sites that are most suitable on request. SEO optimized site's home page, inside pages, making it more relevant. Optimization - internal factor that increases the ability of a website on the first page of search engines.
SEA - « search-based advertising." Site owners to search engines provide the ability to place ads on the first page of requests. This - contextual advertising. It attracts the attention of Internet users. Advertising is issued on request and even helps websites get young customers.
Each search engine for indexing and ranking websites have their own algorithms . If the site is SEO works in Yandex, this does not mean that, for example , Google will react to your site the same way. Then comes to the aid SEA, placing contextual ads on other search engines.
SEM promotes websites for any inquiries and in any search engine , combining the activities SEA and SEO.
Search engine marketing is directly dependent on the context, and is a generic term different ways of marketing sites.