The line of hair above each eye at the bottom of the forehead. They come in all shapes, sizes & styles. It serves the purpose of blocking sunlight from the eyes (notice how the eyes are farther back in the skull). People with darker colored eyebrows usually have better vision on a bright day, seeing as how dark colors (especially black) hold light, while blond might spread light. In my humble opinion, one of the sexiest places to get a piercing. When the two are connected by more hair, it is called a unibrow.

Specifically having to do with the seemingly caterpillaresque collections of facial hair that reside atop one's whites which contain an iris which contain a pupil, which all is inside a socket, which is most commonly part of a face, which also contains some sort of food inhaling mechanism and/or nasal instrument used for sniffing people you want to get to know better, and expelling mucus and other matter. Without eyebrows life would be meaningless and there really wouldn't be reason to continue living once you knew and lost the presence of them in your existence.

meaning thats sick, awesome, totally cool