As temperatures on the U.S. East Coast plummet, neighbors, colleagues, and weathercasters are talking about the ‘polar vortex,’ but what is this phenomenon? Tatiana Schlossberg explains for The New York Times.

First of all, Schlossberg explains, while we may only invoke the name in the winter, the polar vortex always exists. As Schlossberg writes, “That catchy, extreme-sounding phrase is another term for the polar jet streams, which are caused by low-pressure and cold air, encircling both poles. They swirl from west to east, centered around the poles.”

A change of pressure and the resulting dip in the jet stream disturbs the swirl, pushing frosting Arctic air south, usually with a countervailing loop bringing warm air into Alaska or the Arctic.