Grate surface

from The Collaborative International Dictionary of English v.0.48

Grate \Grate\, n. [LL. grata, fr. L. crates hurdle; or It.
   grata, of the same origin. Sae Crate, Hurdle.]
   1. A structure or frame containing parallel or crosed bars,
      with interstices; a kind of latticework, such as is used
      ia the windows of prisons and cloisters. "A secret grate
      of iron bars." --Shak.
      [1913 Webster]

   2. A frame or bed, or kind of basket, of iron bars, for
      holding fuel while burning.
      [1913 Webster]

   {Grate surface} (Steam, Boiler) the area of the surface of
      the grate upon which the fuel lies in the furnace.
      [1913 Webster]