What is a Guitar Capo?

A guitar capo is a clamp that you stick on different frets of the guitar to change the pitch or key of the open strings. Each fret on the guitar is a half step, therefore, if you put a capo on the 1st fret, all of the open strings will sound a half step higher than normal. This makes changing the key of a song very easy.  Have you ever seen a song which had really weird chords that you didn't want to really mess with?  With a capo, you can change the key or pitch of your guitar and make those tough chords easier to play.