Search optimization (SEO) is the process to achieve a higher ranking in search results.
Search marketing (SEM) is a set of activities for increasing website visibility.
Search optimization (SEO)
Search optimization (SEO) is a process of affecting the website visibility (displayability) in "natural" or unpaid ("organic") search engine's results.
Suppose an Internet user types some word or word combination on some search page, for example, "Samsung cell phone" and as a result he/she has got websites with the information about the cell phone Samsung. The user will look through at the most 10-15 pages out of several thousand shown to him/her. I.e. it is important for you to be in these 10-15 sites he will look through. Actions which are focused on being on these 10-15 pages this are the SEO.
Get the top position in Google or Yandex…
Search engine marketing (SEM)
Search engine marketing is one of form of Internet marketing that involves the promotion of websites by increasing their visibility in search engine results pages through optimization (both on the page and out of the page) and also through advertising (paid placements, contextual advertising, paid inclusions). Depending on a context SEM may be a common term for different kinds of sites marketing including the search optimization (SEO) which adjusts or rewrites website content to achieve a higher ranking in search engine results pages or it can contrast with pay per click (PPC), focusing only on paid components.
SEO and SEM in Google
SEM is a promotion of your website in Google usually gives 40-50% of visitors. All other visitors will be able to find offers, goods and services mainly through search engines or search catalogs.
Search requests issued through Google also have a great potential for increasing the number of visitors to your site. These are ads from Google (AdWords) and banners to increase access to your pages.