Backlinks (also “back-links”) are inbound links to a website or web page. A search engine will discover and rank your site based on how many external links to your site it finds from other pages. The PageRank of each site weights the value of the backlink.
Backlinks are hyper-links created using the HTML anchor tag. The syntax of the anchor tag permits the site doing the linking to indicate its relationship to the destination site.
See also PageRank, and no-follow.