ANC
Active Noise Cancellation.
Active Noise Cancellation uses microphones inside and outside the ear cup to detect ambient sound, then plays an inverse waveform to destructively interfere with it. Modern flagships (AirPods Pro 3, Sony WH-1000XM6, Bose QuietComfort Ultra) push the noise floor down by 25-35 dB across most frequencies; bone-conducted speech is the primary remaining leak.