Rockin' Rainbow Dash song :P

The title is a "play-on-words" of the word "hydrocephalus", which is a condition of having too much water or fluid in the brain. The root "aero" means "oxygen" or "air".

Basically, she's an airhead.

"Aerocephalus" by Spyman342
Artwork: "Soaring above the sky" by ZymonasYH
http://zymonasyh.deviantart.com/art/Soaring-above-the-sky-287062539