You’re familiar with the desktop because it’s what you see when you log into your computer with a graphical user interface.
But in terms of a file system, it’s just another directory (usually called
desktop). The only thing that’s special about it is that it’s the one
that is displayed on your whole screen when you use a window-based interface.
This means you can — of course — still access the files on your desktop via the command line.
In most systems you’ll find the
desktop directory inside your
home directory. Your home directory is the one associated with your username,
and which is normally set to be the current directory when you log in. On Unix
systems, this has the special name
~ (tilde, or twiddle).