What’s the Difference Between ‘All-Wheel-Drive’ and ‘Four-Wheel-Drive’?

It's about that time of year again when the roads start to ice up a little bit, it starts snowing on the pass and you want to make sure you're prepared. Maybe you're looking at getting a new car or the one you already have has features you don't even know about. Things like 'all-wheel-drive and four-wheel-drive. They should be the same, right? Not exactly. Here is the difference between them.

All-Wheel Drive (AWD): A drivetrain that employs a front, rear and center differential to provide power to all four wheels of a vehicle.

Four-Wheel Drive (4WD): A drivetrain that employs two differentials and a transfer case to provide power to all four wheels of a vehicle.

-via Edmunds car glossary

Very similar, but how it's executed under the hood is a little different. DigitalTrends can explain it better than I.