Sound is a mechanical wave, in simple terms, pressure displacing and vibrating molecules in a medium like air or water (which is perceived as audible sound). The other type of wave is an electromagnetic wave, which doesn’t need a medium.
Factoids tagged with "Sound"
According to physics, if a tree falls it makes a sound, even if no one can hear it. Sound is a mechanical wave of pressure and displacement through a medium such as air or water. We don’t have to perceive a sound to know the laws of physics are in play.