What is Quattro all-wheel drive in an Audi A4 and how does it work?

I've heard that the Audi A4 has Quattro all-wheel drive, but I'm not sure what that means or how it works. Can someone explain it to me?

Quattro all-wheel drive is a system that distributes power to all four wheels of the car, providing better traction and control especially in slippery or uneven road conditions. This technology was first introduced by Audi in the early 1980s and has continuously improved over the years.