dropped ceilings
Ceiling panels suspended below the structural ceiling to hide lights or utility equipment.
Dropped ceilings are any kind of regular ceiling surfaces installed below the structural ceiling surface, with hollow space between them. They are normally installed to house or to hide mechanical apparatuses such as ductwork, plumbing, recessed lights, fluorescent lights, sprinkler systems, or several of the above. They are often constructed of soundproofing material arranged in an aluminum frame, but may also be plastered or otherwise disguised as true ceilings.
A hollow space separates the installed ceiling surface from the structural ceiling. Concealed service equipment is common but is not required in every part of that space.
The surface can use framed panels or a plastered finish. A visible modular grid is therefore not necessary for the dropped-ceiling designation.