"Workout Splits" are how you lay out your training across the week in terms of what areas of the body you train or what movements you do. The most common are full body, upper/lower, push/pull/legs, and body part splits, but there are TONS of variations of these. 
In this episode, I detail a hybrid split I developed that personally helped me lose 12lb and maintain my muscle mass while adding 20+lb to some of my lifts.