Boiled peanuts are a true Southern tradition. In fact, many non-Southerners have never even heard of them. You'll find bags of hot boiled peanuts at picnics, fairs and, most importantly, at roadstands along country or mountain highways. They're a popular road-trip snack.
Boiled peanuts are simply raw (or "green") peanuts boiled in salty water for hours. All that water makes the shells soggy and easy to break open; meanwhile, the nuts soak in a nice flavor.
Boiled peanuts have been around since (at least) the American Civil War. There wasn't much food around during the war -- especially meat. However, peanuts were in good supply. Soldiers started boiling the peanuts over campfires, and probably added salt as a preservation technique. Peanuts also gave the soldiers a much-needed dose of protein.