Sound is a series of pressure waves/vibrations that can be heard when it interacts with a medium e.g air, sound is a Longitudinal (wave) and there are 4 properties of a wave: Amplitude is the vertical distance from the crest to the centre line of a wave, Frequency is the number of waves passing in a second, Period is how long it takes to do something and Wavelength is the horizontal distance from one wave to another.

The speed of sound is typically 340.29m/s At sea level it is 343m/s.