Where is the Sleep Button?

I have an Inspiron 600m, XP Home et.al. The "easy directions" in Control Panel--Power Options Properties offers three options each for plugged in and battery use. One of the three is What to Do when the Sleep Button is pressed. Where the f..k is that? It is a no brainer to know about closing the lid or pressing the Power Button, but Sleep Button?
What gives here, Mr. Dell?