EVP - (Eletronic Voice Phenomena)
An EVP is a recording of a voice or sound from an unknown source which is heard on recorded data, white noise, audio tape or other electronic media. EVPs are those voices or sounds you do not hear until the media is played after the fact.
One amazing aspect of an EVP is that the voices or sounds recorded sometimes respond directly to the person making the recording.
Most EVPs consist of single words, phrases, or short sentences, although sometimes, they are grunts, groans, growling, or other vocal expressions or sounds such as footsteps or knocking sounds.