When one of the deadliest storms ever recorded in the Southern Hemisphere roared through Mozambique, Malawi and Zimbabwe in March, it was called Cyclone Idai. But the big blow that sideswiped Guam in February was Typhoon Wutip. And if the swirl of nasty weather coalescing over the Gulf of Mexico strengthens as expected this week, it will be Tropical Storm (or maybe even Hurricane) Barry.

What makes a major storm a hurricane, a typhoon or a cyclone? It comes down to location.

They all refer to tropical cyclones — circular storms that form over warm waters, with very low air pressure at the center and winds greater than 74 miles an hour. But different terms are used for such storms in different parts of the world.

The word hurricane is used for the ones that form in the North Atlantic, the northeastern Pacific, the Caribbean Sea or the Gulf of Mexico. Typhoons are storms that develop in the northwestern Pacific and usually threaten Asia.

The international date line serves as the Pacific Ocean’s dividing marker, so when a hurricane crosses over it from east to west, it becomes a typhoon instead, and vice versa.