A key signature is a collection of seven pitches that a diatonic piece of music is composed of. One could think of it as the pitch ingredients within the recipe of a song. As mentioned in my Musical Alphabet and Musical Intervals posts, there are 21 pitches in music. This is a result of a seven letter musical alphabet in which each letter can be either sharp, flat or natural.
Ray Melograne received his BA and ME in music education from Queens College. He is currently teaching music in the NY public schools. He also teaches privately on the Zoen.com network.