Simply put into English, it's a tube that a surgeon runs through your skull and into one of the big, fluid-filled spaces on the inside of your brain (yes, your brain has big fluid-filled spaces on the inside) in order to drain off what's called cerebrospinal fluid. Cerebrospinal fluid surrounds your brain, penetrates it...oh, sorry. *ahem* It does surround your brain, though, and it cushions it and provides a number of different benefits.