A noun meaning a girl who among other things typically wears bows in her hair or thinks its cool to do so. This specific bow-wearing girl is usually found in a suburban setting (this word was created by teens in suburban Washington D.C.). She is likely white, likely an athlete or (more likely) a cheerleader. She is certainly very ditzy, possibly sporting a fake tan, pearls or Tiffany's jewelry and any one of a myraid of painfully adorable designer handbags. She will almost certainly have a very sleek cell phone attached to her head at all times, probably has rich parents and probably has dated most of the football team... twice.
This is a term which describes a broad high school stereotype. It can be used in a derrogatory manner (although not always) it's the sort of thing you might catch the so-called 'geeks' calling you as you drive way too fast out of the parking lot in order to get home in time for the 'OC'.
"That stupid bowhead cheerleader is always making out with what's-his-name in front of my locker... bitch."
"Those idiots may have switched to wearing trucker hats but they'll always be bowheads to me."
"The only thing worse than watching George Bush speak is seeing a bowhead Republican flaunt daddy's bank account."