What is SEO

Easily we can say that SEO stands for 
SEO stands for “search engine optimization.” It is the process of getting traffic from the “free,” “organic,” “editorial” or “natural” listings on search engines. All major search engines such as Google, Yahoo, Bing etc., have such results, where web pages and other content such as videos or local listings are shown and ranked based on what the search engine considers most relevant to users. Payment isn’t involved, as it is with paid search ads.
Search engine optimization is a rising name over the web

Search engine optimization (SEO) is the process of improving the visibility of a website or a web page in a search engine's "natural," or un-paid ("organic" or "algorithmic"), search results. In general, the earlier (or higher ranked on the search results page), and more frequently a site appears in the search results list, the more visitors it will receive from the search engine's users. SEO may target different kinds of search, including image search, local search, video search, academic search, news search and industry-specific vertical search engines.
As an Internet marketing strategy, SEO considers how search engines work, what people search for, the actual search terms or keywords typed into search engines and which search engines are preferred by their targeted audience. Optimizing a website may involve editing its content and HTML and associated coding to both increase its relevance to specific keywords and to remove barriers to the indexing activities of search engines. Promoting a site to increase the number of backlinks, or inbound links, is another SEO tactic.
The acronym "SEOs" can refer to "search engine optimizers," a term adopted by an industry of consultants who carry out optimization projects on behalf of clients, and by employees who perform SEO services in-house. Search engine optimizers may offer SEO as a stand-alone service or as a part of a broader marketing campaign. Because effective SEO may require changes to the HTML source code of a site and site content, SEO tactics may be incorporated into website development and design. The term "search engine friendly" may be used to describe website designs, menus, content management systems, images, videos, shopping carts, and other elements that have been optimized for the purpose of search engine exposure.
The effectiveness of SEO may be measured by the position of a web site on a Search Engine Results Page (SERP) when searching for a certain keyword, or by web analytics Key Performance Indexes (KPIs).