From MEPIS Documentation Wiki
The command line is a type of user interface which allows the user to interact with the computer by typing in commands.
The default application used in MEPIS is the KDE Konsole Terminal Emulator, though many others are available from the repos.
Most new Linux users are reluctant to use the command line at first; it is actually very easy and experienced users will often refer to it as your best friend. You do not need to understand the text in order to be able to cut n' paste it into the box - so long as the person who is telling you what to type understands what they are doing.
Tips and hints
See the UserBase Wiki entry for current Konsole use info.
The command line is also referred to as the terminal, shell, shell prompt, console, or konsole. These terms can be used interchangably.
For more information, consult these pages.