Backlinks or inbound links are links pointing at a particular web page.

The amount and value of inbound links are a primary way that Google places value on your site.

Google measures this value as PageRank.  A web site’s PageRank can bee seen using the free Google toolbar.

The better the inbound links (determined by Google) the higher the PageRank. The higher your PageRank, the easier it is to improve your ranking in Google.