Okk I hope anyone knowing more in linux will post here to clear this thing.
I may be adding to the confusion, but here goes.
Linux, or GNU/Linux operating Systems are basically terminal driven, that is a basic Linux OS will boot into a text based terminal or Command Line Interface, and can use a number of interpreters (the most common being bash - Bourne Again SHell ). On top of this for when a Graphical User Interface is required (GNOME, KDE, XFCE Unity) is the 'X' graphics environment, on top of which will sit a Window Manager (for example KWin as used by KDE). and on top of the Window Manager the GUI Desktop Environment (GNOME, KDE, XFCE Unity LXDE). Sometimes a Linux distro will use only a Window Manager on top of 'X' as the Desktop environment (WindowMaker for example).
When one is using a full desktop version of Linux one will normally be operating in a GUI shell (or Desktop Environment, such as GNOME 3 Shell, KDE 4, XFCE), this is how the majority of Linux users interact with their computer, via a GUI shell in exactly the same way as Windows and Mac users do. Unlike Windows, but similar to Macs, a Linux user has full access to the text based Terminal, either via a Terminal Emulator (which usually loads a BASH interpretor, but can be configured to load any other Interpretor, such as CSH, and many others; Or, and this is where Linux differs from Windows and Mac, directly by using ALT + CTRL + F! .... F6 with F7 to return you to the GUI shell.