The human voice is unique. No two voices in the world are hundred percent alike.
They vary according to physical features like size and form of the larynx and the length and frequency of the vocal chord.
Apart from that, acquired features like dialect, accent, speech disorders or language habits play an important role. This uniqueness is used by SpeakerVerification to carry out a secure and comfortable verification, be it alone or in combination with passwords, passphrases or a PIN.