\Ex`tra*trop"ic*al\, a.
Beyond or outside of the tropics. --Whewell.

From Webster's 1913 dictionary...pretty lame definition if you ask me...

Extratropical is a term used in advisories and tropical summaries to indicate that a cyclone has lost its "tropical" characteristics. The term implies both poleward displacement of the cyclone and the conversion of the cyclone's primary energy source from the release of latent heat of condensation to baroclinic (the temperature contrast between warm and cold air masses) processes. It is important to note that cyclones can become extratropical and still retain winds of hurricane or tropical storm force.