Pitch is the 'high' and 'low', or the 'up' and 'down' of musical notes. Pitches going up or down step by step to make a scale. Put scientifically, pitch is just the frequency of the sound vibration - given in hertz or cycles per second.

Pitches turn into music when they are arranged in some way.

Different pitches one after another can make a melody

Different pitches combined together can make harmony.

If you click on the arrows, you will be able to hear the change in pitch