A suspended floor is when the floor is not directly in contact with the ground and, instead has a ventilated void beneath the floor and the structure is supported on beams. It is possible to insulate the underside of the floor to reduce the heat loss and make it more airtight to reduce the air leakage into the home.
A guide on underfloor insulation has been produced by UK Government that sets out Best Practice in terms of inspection, workmanship and materials.