In construction and architecture, a dropped ceiling, also referred to as a drop or suspended ceiling, is used as a secondary ceiling formed to conceal piping, wiring, or ductwork, into an area called the plenum. Consisting of a grid-work of metal channels in the shape of an upside-down "T", suspended on wires from the overhead structure. These channels snap together in a regularly spaced pattern - typically a 2x2 or 2x4 foot grid in the US or 600 x 600 mm grid in Europe - and each cell is filled with lightweight "acoustic ceiling tiles" or "panels" which simply drop into the grid.