What's the difference between sleep mode and hibernate mode?

Episode 1108
Bruce fromBruce has a computer that he puts into hibernation, but when he unplugs it, it shuts down. Leo says the there's a difference between hibernation and sleep mode. Sleep keeps the computer on, but loads everything into RAM and shuts down the hard drive and other things it doesn't need. It's in an extreme low power mode, but keeps refreshing the RAM so it'll come back on when woken up. Hiberation, on the other hand, completely shuts down the computer and then writes the RAM contents to the hard drive to access when it's turned back on.