You're going to hear the term "polar vortex" a lot this week. It's not a winter storm — but it is what's responsible for freezing temperature across the Midwest and East Coast.

What is the polar vortex anyway? The polar vortex, as it sounds, is circulation of strong, upper-level winds that normally surround the northern pole in a counterclockwise direction. It's essentially a polar low-pressure system. 

These winds tend to keep the bitter cold air locked in the Arctic regions of the Northern Hemisphere. It is not a single storm: The vortex is continually surrounding the Arctic region.

Here's why the vortex matters now: On occasion, this vortex can become distorted and dip much farther south than you would normally find it, allowing cold air to spill southward.