From MEPIS Documentation Wiki
GUI = Graphical User Interface that employs one or more Command line utilities.
GUI vs. Command Line
Many tasks can be done via a GUI (using mouse clicks) but the exact same results could be achieved using Commands entered in the console.
the program K3b is a GUI based on a group of utilities for CD/DVD burning, so with a few mouse clicks you can erase a CD-RW disk
you can use the Command line to issue a command similar to this:
cdrecord -v -speed=10 -dev=ATA:1,0,0 -blank=fast
Use of GUI vs. Command Line is a personal preference, but GUI method is generally considered more user friendly for typical users while use Command Line can be more technical and more dependent on syntax, but many more experienced users consider it easier to use. Using the command line can also be used to troubleshoot problems because any errors will be shown.