I think the intention is to have an active rest week and do something, but lighter/gentler workouts. The first time through I missed that word "active"
and did nothing. Second and third I did cardio workouts that were not too hard, and absolutely no weights or body weight exercises. A lot of people seemed to like to limit the week to yoga, walking, stretch, type workouts. I don't like yoga, but if I did, I would have done a couple days at least of that type of workout.
I did feel really strong after coming back to STS after a week of no weights.