Changes is also a term in
music, particularly in popular, like
jazz, and
blues. The
chord changes.
An example from the blues song Chilly Winds:
C F C C7 F7 Db7 C G7 C
Usually this will be presented above a single line of music. The single line will be the sung, or vocal line--call it the melody.
There will be no left hand, or any instrument part. The changes are to facilitate the artist's musical imagination--to create the comping in the given chord progression, but with complete freedom to improvise and plan a two-handed harmony and rhythm. (I'm thinking of a piano or keyboard.)
The vocalist--if accompanying another--will not want someone stealing his or her melody. And if accompanying onself, one doesn't want something so complicated that it takes up too much attention.
Try singing and playing all by yourself! It's fun, but takes more than a little concentration.