backlink is a text advertisement that is mostly used for rising Page Rank. You can get them by buying them or by exchanging text links.
It's a chunk of html code that looks like this: <a href="http://www.christianlittle.com">My Website</a> Code (markup): But when shown in a web browser, it looks like this: My Website If you get these pointing to your site, it gives you rankings in the search engines.
Google has a piece of software called Googlebot. It's sole purpose is to crawl the web. It jumps from website to website following this links and documenting all of it. It's part of the process that Google uses in their rankings. Yahoo has Slurp! which does the same thing, as does every other search engine.
backlinks are links that link back to your website. It helps becuase Google and other search engines will find these and increase your ranking and domain worth.
Social bookmarking and blog commenting seems to be popular. socialmarker.com socialposter.com setup blogs at blooger.com, wordpress.com and link back to your site. leave your link in your signature file (hint)
it's a link to your site, you can get this by directory submissions, posting ads, blogging and even you can exchange link to other site; but you will propose it. having back links will increase your page rank and your site's quality.
the number of link pointing to your website is called back link. the size of the anchor text does not matter. but u use anchor text tree or four phase keyword.it depend on your business keywords.