1. Any continuous tract or area that differs in some respect, or is distinguished for some purpose, from adjoining tracts or areas, or within which certain distinctive circumstances exist or are established.
2. In geology, any of five great divisions of the earth's surface, bounded by lines parallel to the equator and named according to the prevailing temperature: North Frigid Zone, North Temperate Zone, South Frigid Zone, South Temperate Zone, Torrid Zone.
3. In biogeography, an area characterized by a particular set of organisms, whose presence is determined by environmental conditions, as an altitudinal belt on a mountain.
4. In geometry, a part of the surface of a sphere included between two parallel planes.
5. A specific district, area, etc., within which a uniform charge is made for transportation, mail delivery, or other service.
6. The total number of available railroad terminals within a given circumference around a given shipping center.
7. An area or district in a city or town under special restrictions as to the type, size, purpose, etc., of existing or proposed buildings.
8. Also called postal delivery zone. (in the U.S. postal system) any of the numbered districts into which a city or metropolitan area was formerly divided for expediting the sorting and delivery of mail.
9. In sports, a particular portion of a playing area.
10. A girdle or belt; a cincture.
11. Etymology: from Latin zona, "geographical belt, celestial zone"; from Greek zone, "a belt", related to zonnynai, "to gird".

Originally one of the five great divisions of the earth's surface (torrid, temperate, frigid; separated by tropics of Cancer and Capricorn and Arctic and Antarctic circles); the meaning of "any discrete region" is first recorded 1822.

An area in outer space where sound cannot be transmitted: The anacoustic zone is said to be the upper portion of the earth's atmosphere starting at a hundred miles (160 kilometers) and on into interplanetary space where sound cannot be projected because gas molecules are too far apart to serve as a transferring medium.

The anacoustic zone is also known as the "zone of silence".

The zone of rock flow, as indicated by reactions that may involve decarbonation, dehydration, and deoxidation.

Silicates are built up, and the formation of denser minerals and of compact crystalline structure takes place.

The continental slope; the sea floor from the edge of the continental shelf to the continental rise: The archibenthal zone refers to the ocean layers between 200 feet and 3300 feet (65 and 1050 meters) and is the upper part of the abyssal zone.

The region of maximum auroral activity around either geomagnetic pole within which there is a maximum of auroral activity that lies 10 to 15 degrees geomagnetic latitude from the geomagnetic poles.

1. A term used with reference to the disruption of communications within the auroral zone as a result of the increased ionization in the atmosphere.
2. The communication fadeout in the auroral zone usually as a result of an increase of ionization in the lower atmosphere.

The biogeographic realm of the ocean depths between 100 and 1,000 fathoms (180 and 1,800 meters): The bathyal zone describes the steep descent of the bottom of the ocean from the continental shelf to the abyssal zone.

A layer of the oceanic zone lying below the "mesopelagic" zone and above the "abyssopelagic" zone, at depths generally between 1,000 and 4,000 meters (3,280 to 13,120 feet): The bathypelagic zone receives no sunlight and water pressure is considerable. The abundance and diversity of marine life decreases with depth through the bathypelagic zone and the lower zones.

Demilitarized Zone zone.

The zone of intermediate light inensity in a body of water, with insufficient light for photosynthesis but sufficient light for behavioral responses.

1. The surface zone in a sea or large lake that has sufficient light penetration for net photosynthesis to occur.
2. A reference to the upper layer of a body of water that allows the penetration of enough light to support photosynthetic, or green plants.

The bottom-most layer of the oceanic zone, lying below the abyssopelagic zone at depths greater than about 6,000 meters (19,680 feet); hadal zone: The hadopelagic zone is found in long and narrow topographic V-formed depressions or trenches in the sea. The name is derived from Hades, the classical Greek underworld. This particular layer is 90% unknown and very few species are known to live in the open areas, however many organisms exist in hydrothermal vents in this and other stratums.

1. a painful spot occurring in hysteria which is not a result of an organic disease.
2. An area of the body; such as, the inguinal (groin) and mammary regions which, when pressed, produce hysterical attacks in susceptible individuals.

1. Metamorphism that occurs at or near the earth's surface where it breaks down complex minerals into simpler ones.
2. At or near the earth's surface or the outer zone of the solid earth in which the alterations of rocks result in the production of simple compounds from more complex ones.

It is subdivided into an "outer belt of weathering" and an "inner belt of cementation".

1. The shallow water along the sea shore from zero to the depth where plants no longer root, about ten feet or three meters deep.
2. Also defined as the faunal (animal) zone bounded by the continental shelf; that is, down to approximately 200 meters.
3. Area on or near the shore of a body of water; such as, the region of the shore of a lake, sea, or ocean.

A layer in the mantle between 400 to 700 kilometers across in which there is an increase in seismic velocity because of the phase changes of the minerals present to more closely-packed, denser forms.

The zone in which there is no tidal rise or fall in a system of standing waves, the direction of littoral (coastal or shore region) transport differing on either side of the zone.

1. Water in the ocean which is not close to the bottom: The pelagic zones consist of the waters in a sea that are usually not close to the shores.
2. Etymology: from Latin pelagicus; from Greek pelagikos, from pelagos, "sea, high sea, open sea".

1. Designating or occurring in the shallow-water zone of a sea, over the continental shelf and below the low tide mark.
2. Designating or occurring in the zone of a lake below the littoral zone, to a depth of six to ten meters.

The region of the shore immediately above the highest water level and subject to getting wet by spray or wave splash.

1. A large area of the earth's surface, often spanning continents, in which vegetation with similar characteristics can be found.
2. A plant community which forms regional pagtterns based on the area's geography, geology, and history.

The electrophoretic separation of migrating molecules in a conducting medium which is immobilized onto an inert supporting medium such as paper, cellulose acetate, or agar gel.

Zone electrophoresis allows more manipulation of the separated proteins than moving-boundary electrophoresis.