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.
The "lumberjack squat" isn't what people in the logging industry head off to do behind a large poplar tree after having a hearty breakfast of bran flakes. Instead, it's a helluva' cool squatting movement that doesn't compress the spine.