How does the Audi A8's Active Noise Cancellation work?

I've heard that the Audi A8 boasts Active Noise Cancellation technology. What exactly does this mean and how does it work?

Active Noise Cancellation, also known as ANC, is a system in the Audi A8 that uses microphones and speakers to analyze and cancel out unwanted noise inside the cabin. It works by emitting a sound wave that is the exact opposite of the unwanted noise, effectively cancelling it out.