These are rapid back-and-forth shuttles with one step in between direction changes. Go two steps to the right, then two to the left.
This really focuses on lateral change of direction, and it's a great way to improve coordination and leg strength/power while building structural integrity in the lower body. Higher reps will scorch your quads and lungs.
Hating on CrossFit is trendier than those hipster Ray-Bans your aunt bought you. There are some aspects of CrossFit that deserve your attention, however.