From MEPIS Documentation Wiki
The term Live CD, or LiveCD or Live-CD refers to a CD or another medium (such as USB stick) that contains an operating system that can be booted without installation. This can happen because operating files are placed into temporary memory instead of being located permanently on the hard disk. It is a handy method to demonstrate a new OS without having to install it.
MEPIS provides a LiveCD that is combined with an installer, and was the first Linux distribution to do so.
The Passwords for the MEPIS LiveCD are demo or root. For more information on the LiveCD, see section 3.3 of the User's Manual.