An active recovery aids in alleviating muscle soreness & stiffness by stimulating blood flow and improving circulation to the sore muscles. You don’t want to over exert an already sore muscle, you just want to get the muscle moving to bring a rush of blood and nutrients on the scene.
Examples of an active recovery? If your chest is sore and you’re used to benching 200 on a chest day, bodyweight pushups will be a nice way to loosen your chest muscles up. If your tough chest workout includes bodyweight pushups, try some incline pushups against your kitchen countertop on a day your chest muscles are sore. If you’re sore from running, a great active recovery workout would be a walk or light cardio for 3o minutes.