Desktop Mode is a graphical user interface (GUI) environment for Windows 8 for quickly accessing commonly used applications and services. Desktop Mode works like a typical desktop, as in all versions of Windows earlier than Windows 8, but with slightly different functionality and appearance.
Techopedia explains Desktop Mode
Desktop Mode is one of the two different GUI environments available in Windows 8. The other is the tiled screen menu. Typically, Windows 8 starts in the tiled screen UI, but a user can switch to the desktop mode, which nearly resembles the desktop found in previous Windows versions. However, the desktop mode doesn’t include the start button, although all frequently used apps icons are placed on the horizontal bottom bar. And, unlike the new Window 8 app menu, most of the functionality of desktop mode can be accessed with non-touch input devices such as mouse and keyboard.