|posted: 3/18/2004 at 6:10:24 PM ET|
A key is whatever scale a piece of music is based on. In sheet music you look at the key signature which is at the beginning of the piece to determine the key. It tells you what sharps or flats are in the music, if any. You can also usually look at the first and last notes of the piece to see, but occasionally you can't always go by that. For instance if the first note (or root of the first chord) is F, the piece will either be in F Major or F minor. One way to see which is listen to it. But really you'd better just go back to the key signature I guess, so anyway yeah it helps to know your key signatures to know the key of the piece.
But you simply just asked what a key was, and like I said it's the scale a piece of music is based on (for instance, the key of F Major is based on the F major scale, etc)
I hope that helped.