What does it mean when someone adds ?ref=example.com to the end of a link?

[vinicius]

Someone added a link to my site on their blog but instead of just adding the link, they added a ref link to their site at the end http://mysite.com/?ref=theirsite. com

What does this mean for Google? Do they count this as a clean backlink?

Thank you!

[Claus Mygind]

It is a simple name/value pair using GET the variables are displayed in the URL, it is possible to bookmark the page.