In addition to the term 'mantra,' you will also hear the word Naad in connection with Kundalini Yoga mantras. Naad means "the essence of all sound." It is a particular vibration, a fundamental frequency that comes from one common source or sound current. It is the universal code behind language and therefore behind human communication.
Naad is the glue or medium that connects the little me, the individual, to the Big Me, the Universal Self. It is the vibrational harmony through which the Infinite can be experienced.