On Thursday, temperatures on the East Coast are expected to plummet, and some people — fellow journalists and weather broadcasters, we’re looking at you — may start talking about a “polar vortex.”

We thought you might want to know what the polar vortex is, and what it’s not.

(And we wanted to pre-empt the inevitable chatter about climate change that usually crops up when the thermometer drops — “It’s bone-shakingly cold, how could the Earth be warming?” We’ll tell you how.)

First, the polar vortex always exists. 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.

When a dip in the polar vortex comes to our part of the world, it’s usually the result of a change in pressure, which disturbs the swirl, and can push the frosty Arctic air south, according to Faye Barthold, a meteorologist with the National Weather Service. And the Arctic jet stream (or polar vortex) can sometimes dip far enough south that it allows the cold air to travel down to places that do not normally have Arctic conditions, like wherever you live.