A bed that pulls out from under another bed is called a trundle bed. There. Is no specific size bed just for teenagers, but they usually sleep on twin beds.

A twin bed is usually how we describe a hotel room, this means a room with 2 single beds. Hope it helps, Clair :)

The different beds are: Single bed - for one person. Double bed - for two people. Kings size bed - bigger than a double, for two people. A bunk bed - one bed over the top of another bed, usually both single. Cabin bed - for children, a bed on top of a wardrobe, you get to it with a small ladder (steps)