Loose piece
Loose

When a piece stands en prise implies that it is under attack and endangered to be captured. A piece can only stand en prise when it is valued more than the attacking piece or when it is undefended.
A king can never stand en prise. A defended rook stands never en prise when it is attacked by the queen. It stands en prise when it is attacked by a less valuable chess piece or the queen can get it for free.
It is a little bit old fashioned and distinguished language. It is originally French. I will not use the term unless I speak with someone of who I know that he will like to hear this type of language.
I usually just say "hanged," sometimes "en prise", rarely "loose" and I hope never "hung." Although, since I don't refer to the knight as a horse I suppose hung is not all that bad. I conceptualize the piece being executed due to its owner's carelessness.

Source:http://en.wikipedia.org/wiki/Glossary_of_chess
Loose
piece/positionA piece or position vulnerable to opponent attacks, either because the piece is undefended and cannot easily be withdrawn or supported, or the position isoverextended or its pieces are uncoordinated.
Ergo
Loose is very en prise, loose queen is not well behaved, this is very hard for sanity to push over basic terms after very good joke... Whiskey, honey, call Bourbon, Scotch and Beer...
Do you mean en prise, as in that's a loose piece? Or, do you mean lose, as in getting your butt kicked?