It's known as "active rest". Even though you are not bouncing about in an aerobic studio you can still take exercise on "rest" days. Gardening, cleaning, walking up stairs not taking the list are good examples.
I was having an x ray last Friday and the girl asked if I had impacted the leg? I said god know I would have cried like a girl if I had. To then find myself apologising rather messily to the girl who had asked me.
My body turns 50 this coming weekend, whereas my mind still thinks I'm in my 30s!!! Mid-way through my 12-week training for a marathon in November and its a proper mind-over-matter battle to get out there and do my reps.