When a vibrating object moves forward, it pushes and compresses the air in front of it creating a region of high pressure. This region is called a ____________. 

Sound wave results from the back-and-forth vibration of the particles of the medium through which the sound wave is moving. Because of the motion of the air particles, there are regions in the air where the air particles are compressed together. 

The sound wave consists of a repeating pattern of high-pressure and low-pressure regions moving through a medium. High air pressure regions are called compressions.