A function/shortcut used in the Windows operating system. Pressing the Windows Key and the letter 'D' simultaneously will minimise any folder/program/window that is on the screen at the time.

Due to this function's popularity with risk-taking pornography fanatics (to quickly hide evidence of unscrupulous activity), it can be humorous to shout "WINDOWS KEY D" while entering a friend's room when you know they are using a computer.

Actually, it doesn't minimize all windows, it shows the desktop. There is a slight difference. When you maximize any window, all your former maximized/restored windows will open again. Window Key + M is actually the minimize all shortcut, however if an application has a dialog open, it will not minimize it.