Single-leg running?

I was just reading an article on Competitor.com about anaerobic training and came across this gem:

Few runners care to make time to add plyometrics workouts to their training regimen. But you don’t have to. As an alternative, incorporate some single-leg running into one or two of the runs you’re already doing every week. Start by running on just your right leg for 10 strides and then on just your left leg for 10 strides. Gradually increase the number of strides you do on each leg until you reach 30 strides per leg. You will notice that it gets easier to go longer on one leg, which is a sign that your legs are adapting to the stress and your stride is becoming more efficient. Source

What the heck is single-leg running? Am I the only one puzzled by this? I'm picturing someone running on the track then throwing all their momentum to one side and sort of hopping on one leg until they fall over.