The act of
decreasing the power of your
processor by
drastically
degrading its
speed.
Advantages range from
decreased fan noise (kiss that
processor fan goodbye) and the ability to
emulate your previous computer for
old time's sake, to increasing your
patience quotient and decreasing your
obsession with your little white
box.
Update: Some palm users underclock their machines in order to perserve battery life.
Thanks to spiregrain