Vines is a block added by vanilla Minecraft. It can commonly be found in swamp and jungle biomes. They cannot be crafted and can only be harvested with Shears. Natura adds a Nether version called Thornvines.
They are used in the crafting of Beanstalks. Vines also function as Ladders as long as they're propped against a block. If they're not, they can still be hung from by sneaking while in contact with the vine.