What is the onboard "L" Led?

On my Mega there is a LED labeled "L" that glows orange. What does this mean?

If its like the Duemilanove the 'L' LED is connected to Pin 13 and is widely used by many skeches to indicate something or other. The infamous 'Blink' sketch makes it flash once a second. Or its free for you to make it do what you want.