Headphones with active noise canceling are headphones that reduce unwanted ambient noise. This differs from passive headphones, which, when they reduce ambient noise at all, use techniques such as sound isolation.
To cancel the lower frequencies of noise like human voices of your colleagues, noise-canceling headphones use active noise canceling. They include microphones that measures the ambient noise, generate a waveform that is exactly the negative of the ambient noise and mix it with any audio signal the listener desires. Noise Canceling Headphones specify the amount of noise they can cancel in terms of decibels.