Search engine optimization (SEO) is a series of methods used by content creators to help improve their ranking on various search engines including Google, Yahoo, and Bing. Having a higher search ranking means that people searching for a specific topic will be more likely to see your content before anyone else.
Doing things like giving your content specific titles, using keywords and frequently searched phrases in the body of the page, and maintaining a set of standards across your site are great ways to start with SEO.
More recently, search engines like Google and Bing have started to use social media as part of its search algorithms. Are people sharing your content? Has someone you associate with on Google+ or Facebook shared a specific link related to the subject you're searching for? These may very well be the biggest factors in ranking a site moving forward.