A capo is a device used on the neck of a stringed instrument, such as a guitar, to shorten the playable length of the strings and raise the pitch, effectively transposing the instrument). It is a small device that clamps onto the neck of the guitar and holds down the strings against the fret. The word "capo" comes from the Italian word "capotasto," which refers to what is now known as the nut of the guitar.

Capos are commonly used by guitarists, mandolin players, banjo players, and ukulele players). They are a common tool for players of folk music, such as flamenco, Irish traditional music, and British and American folk music, as well as rock and roll musicians who are influenced by folk and blues). Capos are less commonly used in classical and jazz music).

The main advantage of using a capo is that it allows a guitarist to play a song in different keys while still using first-position open-string chord forms, which have a more droning and fully resonant tone than many bar chords. Capos can also be used to adjust keys to better suit a vocalist or give a song a new vibe.

Capos can be designed to raise all strings or only some of the strings, known as partial capos). Partial capos can create a similar effect to alternate tunings, but there are differences). For example, a common partial capo covers the top five strings of a guitar and omits the bass E string, creating a drop D tuning raised one full tone in pitch when played at the second fret).

In summary, a capo is a device used on the neck of a stringed instrument to transpose and shorten the playable length of the strings, raising the pitch). It is a common tool for players of guitars, mandolins, mandolas, banjos, and ukuleles). Capos are used to change the pitch of open strings without adjusting the tuning keys, allowing a guitarist to play a song in different keys while still using first-position open-string chord forms.