If you're driving in the country and have to stop the car to let a bunch of cows slowly cross the road, you'll be sitting there for a while admiring a herd of ranging — or freely wandering — cattle.
Ranging can describe anything that wanders or varies or moves freely, from chickens to a bookmobile to your own thoughts. Ranging chickens wander all over the backyard, a ranging bookmobile drives from place to place, and ranging thoughts might zing around your brain and keep you up at night. (If ranging thoughts about the ranging chickens keep you awake, consider getting a chicken coop.)