When you wimp out of getting your hair dyed somewhere noticeable and just get one thin streak in the back of your head on the very bottom layer so that when you put your hair into a ponytail you can see it.
Invented by stylists at The Hair Cuttery.
Person 1: Did she get all of her hair dyed?
Person 2: Nah, she just got a fun streak.
Person 1: What a pussy.