Trampoline
A trampoline is a recreational or competitive device designed for users to bounce on.  It normally consists of a metal frame (rectangular or circular in shape) supporting a flat jumping surface connected to the frame by springs.  The jumping surface may be of a strong synthetic fabric material or, mostly, of a mesh design.  Trampolines allow users to bounce higher by storing energy in the springs as they land on the surface which then accelerates the user back away from the jumping surface as the springs contract.