Go to http://www.autoaccessoriesgarage.com/Seat-Covers/
Use the picker to pick a particular make and model: http://www.autoaccessoriesgarage.com/Seat-Covers/_Acura-RDX?...
So far so good, no problem. Your browser now has a cookie that says you're interested in just this make and model. Now for the problem: use the nav links to go to "Cargo trunk liners", and where do you land?
http://www.autoaccessoriesgarage.com/Cargo-Trunk-Liners
That's cloaking -- it's not showing you all of the liners, just the ones relevant to the make and model you picked earlier. Instead, the site should add _Acura-RDX?year=2008 to the url, just like before.
Why do search engines care about this stuff? Now imagine you type in [auto accessories cargo trunk liners] into your favorite search engine, and the result is http://www.autoaccessoriesgarage.com/Cargo-Trunk-Liners ... what does the search engine think you'll see? It has no idea, really.