A rover is a drifter or wanderer, someone who doesn't settle in one spot. If you grow up in a small town, you may dream of buying a camper and living as a rover one day.
Because rovers tend to roam around, this word has historically been a popular name for dogs. In fact, Shakespeare even called a dog Rover in A Winter's Tale. The rover vehicles used to explore rough terrain got their name from this same sense of wandering. Planetary rovers roll around the surfaces of moons and planets, exploring on their own or carrying crew. Land Rovers and other cars bill themselves as equally rugged and adventurous.