Terrain, or relief, is the third or vertical dimension of land surface (aka "up and down" dimension.) When relief is described underwater, the term bathymetry is 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 is used as a general term in physical geography, referring to the lie of the land. This is usually expressed in terms of the elevation (height of the land,) slope (angle of the elevation,) and orientation of terrain features. Terrain affects surface water flow and distribution. Over a large area, it can affect weather and climate patterns