Search engine optimization or SEO is optimizing a web site to achieve higher rankings in web search engines. An individual wants to get web traffic to their web site for whatever reason, many times to sell or offer services. Consumers of goods or services need a way to find the product. The owner of the website will build content and use keywords, words that correlate with the content of the web site. The searches are to be unbiased in other words it is algorithmic or organic. This insures fairness and requires that web site owners actually use keywords that reflect the content of their website. Google is a big player in search engines and website owners loaded up content with keywords simply to get traffic to the web site for ad clicks. The keywords did not have much in common with the web site content.
Google changed all that by changing their algorithm, which simply means it redefined the search engines instructions on how to conduct the search. This made searches more defined more definitive, closer to what the searcher actually wanted to find. This forced website owners to have solid content reflective of the keywords, which should have been the goal all along according to many. The rule of thumb is one page of content for every keyword or keyword family chosen.
If the web site sells books then, a keyword family might be books for sale or a sale on books. The web site is about books, but books may not be for sale, so it is important the keywords reflect what is actually going on. Books for sale should be one page of content and books are bought an entirely different page. The keyword books will not gain a high ranking, or indexing in search engines meaning the web site has not been search engine optimized.
Google by changing their algorithm stopped the keyword abuse and HTML source abuse to gain a higher ranking. Well-informed web site owners knew the system and loaded up poor content with keywords that had no relationship with the content simply to get traffic there for ad counts. This was unfair to ones that had solid content but could not get a higher ranking because keyword stuffers had gained all the top rankings.
Search engine optimization uses keywords that reflect the content of the web site, so anyone searching for books for sale will find books for sale. Web site owners can get a Google adsense account free with Google analytical to track where traffic comes from and how traffic is directed to the web site. Owners can then update their content or try various other keywords or tag lines. Search engine optimization requires exploring what works best for that web site. Now that the playing field is somewhat leveled as far as rankings go everyone can build solid content and over time can expect solid rankings and an increase in web traffic.