"Rest days" refer to designated days when one takes a break from their regular activities and work in order to relax, recover, and recharge their energy. Full definition
On rest days take any time of the day with 16 or more ounces of water. (olympus-labs.com)
Make sure you take rest days between, and if you're feeling sore, give yourself 48 hours of recovery before doing this workout again. (mindbodygreen.com)
This is why it is important to have a couple of rest days in between. (gymjunkies.com)