If you open nautilus and browse to the root filesystem, you’ll see something that looks like the image to the left.
This is the default layout of the filesystem in Ubuntu 10.10, and is a peek into the ancient (by computer science standards) history and genealogy of Linux. The directories listed above are holdouts from one of the oldest standards, the Filesystem Hierarchal Standard, FHS. FHS is the system that defines what belongs where. Here’s a quick rundown of the default Ubuntu filesystem: