Geographically, the imaginary great circle of latitude 0o on the earth's surface, which is equidistant form the poles, and which separates the Northern Hemisphere from the Southern Hemisphere
Intergovernmental Oceanographic Commission IOC technical series 37, Tsunami Glossary (A glossary of terms and acronyms used in the tsunami literature - English), , United Nations Educational, Scientific and Cultural Organization UNESCO, Paris, France 1991. http://unesdoc.unesco.org/images/0008/000885/08853 8eb.pdf, (ND/ Tsunami Sci - Brit) {590}