Search Engine Optimisation (SEO) can be defined as:
“The process which aims to get websites listed prominently within search engine’s organic (algorithmic, spidered) search results.” (Internet Advertising Bureau, 2011)
The search engine’s organic listings, as the IAB mention above can also be known by a number of different names, with many people calling them the natural listings. You may also hear people refer to the search results (including the PPC ads) as the SERPs (search engine results pages).
As you can probably imagine, the higher a site ranks in the search engines the more visitors they are likely to receive (and more they could potentially charge for advertising) and so the idea of optimising sites and improving their visibility became a very strong lure to the early webmasters and so the concept of optimising sites came into existence.
There are hundreds of different signals that Google and the search engines use in their ranking/search algorithms, including how easy a site is to use, the specific content of the site (the use of relevant keywords within the copy as well as source code of the pages) as well as a number of off site aspects.
Google provide lots of documentation on SEO with their Webmaster Central resource being a very good starting place if you’re interested in learning more about the subject.
If you are interested in chatting with me about SEO please contact me via the various channels mentioned on this site, or if your interested in hiring a SEO specialist for your business please feel free to fill out the contact form on the Screaming Frog site and we can get back to you.