SEO means search engine optimisation. It is done so that the website is given good ranks and comes on the the top ten results of various search engines like google, yahoo and bing. Bing is also very famous as it is Microsoft's answer to search engine.
Everyone wants to be on the top to be famous and also to lead others. And in case of website it is very easy to be on the top of search engines just by choosing effective SEO services. It makes your products much more searchable and at the same time also helps to expand your business. Not only big companies, but small growing up businesses are also looking for SEO to be done to their website to have a good rank and opinion about their services.
SEO should be done by people practicing white hat methods and not black hat. It is really essential otherwise the website would not rank as you would expect.