Terrain, or relief,'s the third or vertical dimension of land surface. When relief's described underwater, the term bathymetry's used. Topography has recently become an additional synonym, though in many parts of the world it retains its original more general meaning of description of place. Terrain's used as a general term in physical geography, referring to the lie of the land. This's usually expressed in terms of the elevation, slope, and orientation of terrain features. Terrain affects surf… (More on Terrain)