If your question relates to the drop ceiling type, the grid is the metal strips thet hold the ceiling panels . usually 2'x4'
Do you know what a drop ceiling is? The tiles fit into the ceiling grid
A metal grid work structure that ceiling tiles are attached to. See them in commercial buildings and when people finish off their basement ceilings. The grid allows you to pop out a ceiling tile and access pipes, wires above the grid. Can also pop in flourescent light fixtures.
It is the frame work for a suspended ceiling. Metal channels are suspended from tie wires in a grid pattern and ceiling tiles are dropped into the grid.
