Noise-cancelling headphones are headphones that reduce unwanted ambient sounds using active noise control. This is distinct from passive headphones which, if they reduce ambient sounds at all, use techniques such as soundproofing.
Noise cancellation makes it possible to listen to music without raising the volume excessively. It can also help a passenger sleep in a noisy vehicle such as an airliner. In the aviation environment, noise-cancelling headphones increase the signal-to-noise ratio significantly more than passive noise attenuating headphones or no headphones, making hearing important information such as safety announcements easier. Noise-cancelling headphones can improve listening enough to completely offset the effect of a distracting concurrent activity.