Definitions for "Sound Waves"
Longitudinal pressure waves in any material medium regardless of whether they constitute audible sound (earthquake waves and ultrasonic waves are sometimes called sound waves).
air vibrating
vibrations of molecules transferred in ''waves'' through either a gas, liquid or solid; in order for sound to exist, molecules must be present and the molecules must have a source which starts them to vibrate - passing their vibrations outward and in successive waves. In a vacuum (like in outer space), sound cannot be produced nor transferred.