A digital elevation model (DEM) is a digital file consisting of terrain elevations for ground positions at regularly spaced horizontal intervals. (A commercial definition - new technology)
Lynn M. Highland of USGS and Peter Bobrowsky of Geological Survey of Canada, U.S. Department of the Interior, U.S. Geological Survey USGS,Circular 1325, The Landslide Handbook (a Guide to Understanding Landslides), Appendix A: Basic Information about Landslides Landslide, Part 1: Glossary of Landslide Terms, Washington, DC, USA 2013. http://pubs.usgs.gov/circ/1325/pdf/Sections/Append ixA.pdf, (ND/ Lndsld - Amer) {924}