The simplest answer to this question is: sound is what you hear. However, if you want to define it properly, it’s less straightforward than that. Sound is characterised by two aspects: a physical and a sensory aspect. In terms of physics sound is produced by a source that is caused to vibrate. This vibration results in variations in air pressure. The sound spreads through the air as waves. The sound waves are picked up by our hearing and recognised as sound (the sensory aspect).
Everyone knows examples of sound sources caused to vibrate. Here are a few:
- Vocal chords that start vibrating, when we sing or talk
- The engine of a car driving past
- A saxophone you blow into
- Clicking heels on a wooden floor
Sound is usually picked up by our hearing through the air, but it can also move through a different medium, such as water. In short: sound is produced by a vibrating source; the vibrations are spread by a medium (usually air) and are subsequently picked up by our hearing and recognised as sound.