A word of many meanings. Usually used to show agreement/excitement towards a suggestion made by a friend. Also can be said (quickly) when something is said that you couldnt be less interested in and you have to say something to at least show you were listening.
"Dude..what if we crushed these brews THEN hit the movies with 10 sexy ladies..." EYAHH!!!!
"Did you know the sun is gonna be bigger than usual today because of the earths abnormal rotation?" ........ "eyah" (said very quickly/softly)