As it relates to playing music, pitch is a property of sound that allows us to judge one tone as 'higher' or 'lower' than another.
One of the most basic pitch skills for a musician is using the voice to match pitch with a given note. That is when a not is sung or played on an instrument, the musician then sings back the same pitch.
A second fundamental pitch skill involves pitch comparison. Given two notes, a musician should be able to quickly determine which of the two is higher in pitch.
By developing these skills, the musician will be able to sing and/or play 'in tune' more easily and with greater accuracy.