The state or condition of having something up your ass. Most often used in reference to the location of a stupid person's head.
Origins: The term "defilade" is used in military tactics to refer to a position where natural surroundings protect units, vehicles or equipment from enemy fire.
Sgt. Slaughter: "Private Pile might be the stupidest person in this company. His head is so far in rectal defilade that he can see his own teeth."
A "Picki Defile" is when your raid wipes due to a single person placing the defile on top of a ton of people (usually near the middle of the platform) when facing the Lich King 25 (Normal OR Heroic) encounter.
Ah wow Guin, sick Picki Defile thanks, just wipe it guys...
I spent some time yesterday cleaning, as the inevitable accumulation of detritus (and filth) had reached a breaking point, and some serious defilthification was necessary.