Magic Smoke: A mythical substance which is supposedly vital to the functioning of electronic equipment. Therefore when the magic smoke escapes, the equipment stops working. The term is often heard when some hapless fool wires equipment up backwards or to the wrong voltage causing the circuit board to fry. Upon bewildered enquiry, some smart-ass usually quips "Ah, you've let the magic smoke out", "Idiot, you've let out the magic smoke". Adapted from the Urban Dictionary.