A debian based live CD.
This means that the linux will boot and run off the CD and in memory, usually without needing to write to the system hard-drive. These are useful as system recovery disks, linux demo's, hardware compatability tests or even to install to hard-drive as a lightweight distro. These live distros analyse and configure hardware as the system boots, and usually manage to provide network connectivity, an X server, a desktop manager and applications like system and office tools. On average hardware (e.g. AMD500 / 128MB RAM) this boot and configure process can take as little as 2-5 minutes.
There are many derivatives of Knoppix, like Kanotix and many others. These are oftem customised for Locality (language), or towards a particular desktop manager system (Gnoppix). One derivative- DamnSmallLinux, is optimised for space (50MB iso).