Backlinks

• A backlink is whenever a link to your website shows up somewhere else on the Internet. You could have a link to it on a social-networking site, placed in a forum or even mentioned in an article. All of these links point out to a search engine that your website is popular and, as such, it should rank more highly in a search-engine queue.
  
  

Diversity

• Diversity in your backlinks means that you have them in different places. For instance, you could have a backlink to your site on a Facebook profile, an Internet bookmark in a social-networking site or have it listed with an image placed on a Flickr account. The variety of different types of bookmarks you have makes your backlinks come up as more relevant, because they're found in text, image, video and on websites that have different flavors. The translation is that your website seems more popular across the board.
  
  

Quantity vs. Quality

• The more backlinks you have, within reason, the better off you are. The maximum exposure that you can gain is always good, and if you have dozens of websites where searchers can find your website, then you'll increase your traffic. However, quality is also measured by a search algorithm. If you have a website about religion and it's linked by a website also dedicated to religion, then that's considered a better-quality link than if your friend posts a backlink on his site dedicated to helping kittens. The closer the topics and keywords are, the better the quality will be.
  
  

One Building Block

• Backlinks are just one component of SEO. You should also select the proper keywords at the right density to catch attention, and you need to pick catchy subjects that people are looking for. It doesn't matter if you have dozens of backlinks if you didn't use any easily searchable keywords and your website is about an extremely niche subject. SEO has to be taken as a whole, but that's no reason not to get all the quality backlinks you can.