What is a tropical depression?

A tropical depression is an organized system of clouds and thunderstorms with a defined, closed surface circulation and maximum sustained winds of less than 17 metres per second (33 kn) or 38 miles per hour (61 km/h). It has no eye and does not typically have the organization or the spiral shape of more powerful storms. However, it is already a low-pressure system, hence the name "depression".

Tropical Depression are normally a storm with a wind below 34 Miles per hour Tropical Depressions are Disturbances to the united states. Tropical Depressions are Called this because depression is a down graded and was called this from the International Oly Metorology ( I think i got the O incorrect) So its called the IOC who directs the united states to be calling them that It is not are fault as long as your not near one they just feal like a wind storm regular

A tropical depression is defined as an area with low air pressure, high winds, thunderstorms which can potentially be a precursor to a cyclone forming. In developing tropical cyclones, strong thunderstorms occur. Air pressure drops at the surface of these storms. This low pressure attracts warm moist air from the ocean's surface.

(meteorology) a region of low pressure that develops into a hurricane or tropical storm

http://en.wiktionary.org/wiki/tropical_depression

http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hurr/...

A tropical cyclone in which the maximum sustained wind speed (using the U.S. 1 minute average standard) is up to 33 kt (38 mph, 17 m/s). Depressions have a closed circulation.

http://www.aoml.noaa.gov/hrd/tcfaq/A5.html

What causes it?

http://www.answers.com/topic/tropical-cyclone

A depression is a region of lowered atmospheric pressure. It is due to turbulence in the atmosphere caused by uneven heating and eddy currents caused by the Coriolis effect.