What is a Digital Elevation Model (DEM)?
Digital Elevation Model. (Also DEM, DTM, Digital Terrain Model). A digital representation of the elevation of locations on the land surface. A DEM is often used in reference to a set of elevation values representing the elvation at points [or pixels] in a rectangular grid on the Earth’s surface."
Source: McDonnell, Rachael and Karen Kemp. International GIS Dictionary. Geoinformation International, 1995.