Modern ropes are known as kernmantle ropes. The kern is the inner core of the rope and the mantle is the braided sheath. The mantle protects the kern from damage due to abrasion. Single, Double, or Twin Single ropes are the simplest rope to climb with, and the lightest. A single rope is designated by a circle with a 1 in it on the end of your rope.
Most climbers use single ropes for climbing.
Single ropes the most common type of dynamic rope on the market, and the most widely used. The benefit of half ropes becomes evident when your route wanders all over the cliff. A single rope will put a great deal of friction in your system, which feels like you re climbing with a Mac Truck on your harness. In contrast, half ropes allow you to stagger the ropes in your protection, reducing the amount of friction. They are also a backup in case one rope gets cut in a rock fall or by being stepped on by a crampon.