An excersise that tones and strengthens the users core abdominal muscles. You lie down on your front supported from touching the floor by your forearms, your feet assume the position they would if you were doing press-ups (push-ups US) You must then remain in the position, without allowing your body to sag for as long as possible.
As this is a timed excersise it is often used as a competition between people - whoever can do it for the longest time wins! Anything above 3 minutes is good, 6 minutes excellent.
Joe: I love Jayne!
Tom: Me too, we must battle to the death for her heart
Joe: I too, wish to win the heart of Jayne, but death would not be adequate for her heart... We must perform... THE PLANK!!
Tom: Lets do this!