Search Engine Optimization, SEO for short, is a process that advances your website so it could be found on the Internet by your customers. Unlike, paid search (see another section), SEO is organic or free in nature. SEO applies to any content that a producer makes; a website, blog, or even a video. Google, Bing, and Yahoo are the three most popular search engine sites and their respect for your content is a constant earning of trust.
Each search engine has its own algorithm that is used to rank your content to determine its worth to an enquirer. There are known tricks that can boost your ranking and there are some tricks that are only known by professionals. Here is a good video that explains the process in detail.