A divan guest bed has a smaller bed stored within the divan base. when pulled out it will raise to the same height and used as a single bed or put at the side of the divan set to create a larger bed.
Wooden or metal framed guest beds have a trundle be stored underneath that is generally the same size as the main bed.
Folding guest beds have a foam or sprung mattress on top of a sprung slatted base. When folded in half it can be stored out of site when not required.