From our good friends at Wikipedia:
Evaporative coolers (also called air, swamp, or desert coolers) are cooling devices which use simple evaporation of water in air. They differ from refrigeration or absorption air conditioning, which use the vapor-compression or absorption refrigeration cycles. In the U.S., small-scale evaporative coolers are called swamp coolers by some users due to the humid air conditions produced. The name sump cooler is also used. Air washers and wet cooling towers utilize the same principles as evaporative coolers, but are optimized for purposes other than air cooling.
Evaporative cooling is especially well suited for climates where the air is hot and humidity is low. For example, in the U.S., the western/mountain states are good locations, with swamp coolers very prevalent in cities like Denver, Salt Lake City, Albuquerque, and Phoenix, where sufficient water is available; in Australia, evaporative air conditioning is popular in Perth. In dry climates, the installation and operating cost of an evaporative cooler can be much lower than refigerative air conditioning, often by 80% or so. But evaporative cooling and vapor-compression air conditioning are sometimes used in combination to yield optimal performance. Some evaporative coolers may also serve as humidifiers in the heating season.
Did I ask? Far be it for me to ask a question before doing research on my own. I already got an asshole, don't need another one ripped.