What is sleep?

Sleep is the experience of being unaware that you have slipped into engagement in a bizarre disjointed video game with large down load gaps.

Sleep is Stand By Mode for humans.

Which is what I'm going to do now.

Sleep is putting yourself in airplane mode.

Sleep is recharge time, and while you're recharging, your hard drive is checking itself for anomolies.

Macbeth, Act II, Scene 2.

Sleep is the time when your conscious mind lets go, and the parts of your brain which are not conscious sort through the input received while you're awake. Sleep is a time when there are characteristic grain wave patterns, some of which are associated with rapid eye movements, when we dream. You interfere in sleep and dreaming at your peril.

I always loved that "reveled sleeve of care" line.

Here's some more of old Snakeshit, from Hamlet, Act III, scene one (rendered into modern English):

To die, to sleep—
No more; and by a sleep, to say we end
The Heart-ache, and the thousand Natural shocks
That Flesh is heir to? 'Tis a consummation
Devoutly to be wished. To die, to sleep,
To sleep, perchance to Dream;
Aye, there's the rub,
For in that sleep of death, what dreams may come,
When we have shuffled off this mortal coil,
Must give us pause.

Sleep, is when the biologic machine, converts it's food to potential energy, as an electric car must recharge it's batteries.

Ayup. Willie the Shake says it best.

Is he related to Shakes the Clown?

Sleep is some kind of repair and maintenance process, but it seems to be more than just a simple repair and resetting of physical systems. When you first go to sleep, your brainwaves show the kind of slowing down one would expect, but after about 90 minutes, your brain waves become active again and it doesn't mean that you're waking up. This is when dreams occur. It is likely that sleep serves several purposes at once of which simple repair and reset constitute just one.

"Sleep" is wha tha womans put on under der dress wha keep the woman body from show though der dress. Some time a wise guy say to woman, "Hey, your sleep is showin'."

Sleep is when the aliens plug into your ear and reprogram your brain. Or at least that is what the Discovery channel says.

sleep is the state in which your brain and the rest of your body renegotiate terms.