This article is from the Storms FAQ, by Chris Landsea email@example.com with numerous contributions by others.
The terms "hurricane" and "typhoon" are regionally specific names for
a strong "tropical cyclone". A tropical cyclone is the generic term for a
non-frontal synoptic scale low-pressure system over tropical or sub-
tropical waters with organized convection (i.e. thunderstorm activity)
and definite cyclonic surface wind circulation (Holland 1993).
Tropical cyclones with maximum sustained surface winds (see note
below) of less than 17 m/s (34 kt) are called "tropical depressions".
(This is not to be confused with the condition mid-latitude people get
during a long, cold and grey winter wishing they could be closer to the
equator ;-) Once the tropical cyclone reaches winds of at least 17 m/s
they are typically called a "tropical storm" and assigned a name. If
winds reach 33 m/s (64 kt), then they are called: a "hurricane" (the
North Atlantic Ocean, the Northeast Pacific Ocean east of the dateline, or
the South Pacific Ocean east of 160E); a "typhoon" (the Northwest Pacific
Ocean west of the dateline); a "severe tropical cyclone" (the Southwest
Pacific Ocean west of 160E or Southeast Indian Ocean east of 90E); a
"severe cyclonic storm" (the North Indian Ocean); and a "tropical cyclone"
(the Southwest Indian Ocean) (Neumann 1993).
Note that just the definition of "maximum sustained surface winds"
depends upon who is taking the measurements. The World Meteorology
Organization guidelines suggest utilizing a 10 min average to get a
sustained measurement. Most countries utilize this as the standard.
However the National Hurricane Center (NHC) and the Joint Typhoon
Warning Center (JTWC) of the USA use a 1 min averaging period to get
sustained winds. This difference may provide complications in comparing
the statistics from one basin to another as using a smaller averaging
period may slightly raise the number of occurrences (Neumann 1993).