Sheet

Any material or piece of uniform thickness and of considerable length and width as compared to its thickness. With regard to metal, such pieces under 6.5 mm (1/4 in.) thick are called sheets, and those 6.5 MM ('/4 in.) thick and over are called plates. Occasionally, the limiting thickness for steel to be designated as sheet steel is No. IO Manufacturer's Standard Gage for sheet steel, which is 3.42 mm (0.1345 in.) thick.

Source: The OHIO State University