Dynamic Directories??

[justkyle]

I've got a burning question that I gotta have answered. How do sites such as flickr work when you type in flickr.com/photos/<em>kylejones/</em> . Is there actually a directory labelled kylejones in flickr's database, or is it just a way of passing variables around and such. I think it's the ladder, but if anyone can point me in a direction for implementing this, it'd be MUCH appreciated.