Backlinks are one of the most basic forms of search engine optimisation that determines how high your site is ranked on search engines. To put it simply, a backlink is a hyperlink leading to a part of your web site, showing the content you have there.
The parameters of backlinks are one of the most important factors that Google uses when sorting out page rankings. Other search engines use backlinking too to sort sites out, but seeing how Google holds most of the search engine market, this tells how much good backlinking is important. Not so long ago when Google was fresh, it was enough for you to ask another webmaster to link to your content and he would link back to you and that would give both of you a bit of a ranking boost, but Google has grown smarter over the years and now web crawlers can recognize backlinks that are used in this way, and not as part of quality of content.
Also, the rankings of the site that you are getting linked from used to not be important, but now that and the volume of traffic coming in through that link are key factors in determining page rankings. It is much better to have 10 high quality backlinks then 100 of low quality ones as far as Google is concerned, and that’s what makes social and viral marketing so important, it gives you a good ranking boost and lets you have plenty of internet exposure, giving you a chance to present your ideas or sell your products to more and more people.
While backlinking is something you will definitely get if you pay for a quality SEO, with some effort and social interaction, you can do an average job yourself, it just takes time and a lot of effort.