CrossFit Open 18.0 Workout

The 18.0 CrossFit Open Workout is…

21-15-9
Dumbbell snatch
Burpee

Movement standards:
All athletes will only be allowed to switch hands on the way down, once the dumbbell has passed beneath eye level.
Feet must be kept together on the burpees, any stepping will render the workout scaled.

What is 18.zero?