It's common to have rest days. In order to gain strength, get faster, have more endurance -- any physical goal -- the body must recover. So periodically, you need to "rest" and give your body time to heal itself and grow stronger. Some people train every other day, some 2 on, 1 off -- there are endless variations. But at some point there needs to be "hard" day and "light" days, and usually some days with next to no major activity. Roger Bannister rested for the 5 days prior to running his world record breaking sub 4:00 minute mile!
But rest does not have to mean no exercise. Active rest can be just as beneficial, and sometimes even more so. An active rest day is where you plan on moving the body through some range of motion but nowhere near the intensity (or volume) that you would approach on a normal workout. If your strength training workouts usually move 2500 lbs of iron on average then an active rest day of 1000 pounds may be enough to keep the pump primed and the body responsive. If your light runs are at a 10:00 min mile pace then brisking walking at 4-5mph for 30 minutes or so would be active rest.
There are many benefits to active rest, and the largest being psychological. Sometimes we are so worried about "losing it" that there is a constant urge to be doing something. But the body needs time to recover. So an active rest day may be just enough to satisfy the inner critic and still give yourself the needed time to repair and rebuild.
