What do you understand by a sound wave?

A sound wave is the pattern of disturbance caused by the movement of particles traveling through a medium (such as air, water, or any other liquid or solid matter) as it propagates away from the source of the sound. The source is some object that causes a vibration, such as a ringing telephone, or a person's vocal chords. The vibration disturbs the particles in the surrounding medium; those particles disturb those next to them, and so on. The sound waves travel in medium through compression and rarefactions.

Sound waves are Longitudinal Waves which means that particles of the medium moves in the direction of propagation of the wave. The figure below depicts how the sound wave travels.