The Dictionary defines sound as a vibration that travels through air or another medium and can be heard when they reach a person or animals ear.
I think this definition does not do enough to describe sound, because sound is nothing more than an energy wave which is created by a vibration. What we perceive as sound, is simply what happens when our ear drums vibrate in response to coming into contact with those energy waves emitted from the source.
More simply, sound is a form of energy caused by vibrations (Back and forth movements of an object).
These vibrating waves of energy we call sound waves, spread from the source in a pattern we call a frequency. When the object vibrates, it causes the air particles around it to move, these air particles are measured to determine the frequency. The faster the vibration, the higher the frequency, and the higher the pitch we hear as sound.
Sound can travel through solids, liquids and gases. Solids are made of tightly packed, dense particles, so they absorb vibrations in the particles much faster. Therefor, it goes that sound travels much farther when it travels through air and liquid.
This simple photo from Encyclopedia Brittanica provides an easy visual to demonstrate.
This great video has some excellent visuals to give you a greater understanding of sound. The video defines sound as more of a disturbance in the air pressure as a result of a vibration.
Whether you begin to understand sound as energy, a vibration or a disturbance of the air waves caused by the vibration, my goal here is to merely get you thinking about sound. Because as we go along with these posts, I am really going to ask you to really keep an open mind and start to think of sound differently. As we go, I hope to convince you of the many applications of sound, once we start to view it differently.