Tropical Terminology

CYCLONE
Low pressure system that has a “closed” (fully circular) wind circulation, as compared to a tropical wave, which does not.

TROPICAL LOW

A tropical low pressure system.   Typically the term is used for a weak one which is not yet, or is no longer, a tropical cyclone.

REMNANT LOW

A tropical low which used to be a tropical cyclone.

EXTRATROPICAL CYCLONE
A non-tropical cyclone.   A typical cyclone in winter over the United States is an extratropical cyclone.  

Tropical cyclones often become extratropical, undergoing “extratropical transition,” as they move out of the tropics; and once in a while an extratropical cyclone can transition into a tropical one.


POST-TROPICAL CYCLONE

As the prefix suggests, a former tropical cyclone -- which has either become extratropical or a remnant low.


SUBTROPICAL CYCLONE/DEPRESSION/STORM

A type of “hybrid” that has characteristics of both tropical and non-tropical cyclones.

 
http://www.wunderground.com/blog/stuostro/comment.html?entrynum=31