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.
Bill swifty entered Scott's room while shouting "WINDOWS KEY D" (windows key + d) to find Scott abusing himself with the GIF section of 4chan.org displayed on his monitor.
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.
Keyboard shortcut for bookmark, often used by local Indonesian forum users which had not enough time to read and the user used it to inform the thread starter that they will read it at the later time.