The term "isolation" refers to how well the earphones physically filter out ambient noise. Tips that go into your ear canal are far more effective at isolating than ones that stay outside. Noise cancellation, also known as Active Noice Cancellation or ANC, occurs when an earbud produces a tone that is the inverse of the noises around you, thereby canceling the noise and providing silence. Noise cancellation generally necessitates a mix of isolation and ANC.