What is SEO
Search Engine Optimisation (SEO) is the process of setting up your website and respective web pages so that they rank well for a particular search term (or keyword) within the organic (natural or editorial) listings on the Search Engine Results Pages (SERPS) of major search engines such as Google, Bing and Yahoo.
In the past it was much easier to gain number one rankings on Google by applying some basic on and off-page tactics as search engine algorithms were much easier to crack than today. In the past, applying the target keyword all over your web pages and getting lots of links was enough to achieve top rankings.
These days, search engine algorithms have become much more complex – Google has over 250 variables that it applies to determine where web pages should rank when someone types in a particular search query. Search Engines have also become a lot better at finding web spammers and can very quickly detect if someone has tried to manipulate the system un-naturally to gain top rankings. As the market becomes more aware of the benefits of natural traffic from search engines, the more competitive it becomes to rank for targeted search terms.
Broadly speaking, Search Engine Optimization includes the practice of applying on-page and off-page (also known as on-site and off-site) principles to web pages in order to improve the rankings of key web pages on the Search Engine Results Pages. On-site SEO elements refer to the architecture and online copywriting applied to each web page to rank for targeted keywords. Off-site SEO factors refer to the links and citations that these pages receive from contextually relevant, complementary authority websites, where the link references the keywords to further reinforce the popularity and relevance of the linking page.
Learn more about SEO on Wikepedia.