1. A method for expanding the user's workspace beyond the boundaries of the computer screen. The desktop may be scrollable left and right, up and down, as if a larger desktop were positioned behind the glass screen and moved around to reveal icons, windows and other objects that were 'off-stage', or out of view. Alternatively, as with the KDE desktop, multiple buttons may be available, each of which displays an area of desktop equal to the size of the glass screen and which can each contain different objects. From I-gloss

2. A way of reducing clutter on your screen by expanding the available space beyond the actual screen boundaries. From Linux Guide @FirstLinux