What is a backlink? The quick answer: backlinks display other webpages that link to your posts.
Backlinks enable you to keep track of other pages on the web that link to your posts. For instance, suppose John writes a blog entry that Mary finds interesting. John then goes to his own blog and writes a post of his own about it, linking back to Mary’s original post. Now Mary’s post will automatically show that John has linked to it, and it will provide a short snippet of his text and a link to his post. What it all works out to is a way of expanding the comment feature such that related discussions on other sites can be included along with the regular comments on a post.
Just a quick example: Go to google and type your full URL with the link: preceeding to it (link:www.yourdomain.com) in the search box and hit enter. The results you get will give you an idea of how many links are being pointed to your website. This is a very rough estimate of links pointing to your website but you can always refine your search by using google advance operation.