The term 'Guitarist's Aid' refers to three items that are commonly used by guitarists: a CAPO (4 letters), an amp (3 letters), and a STRAP (5 letters). A CAPO is a device that clamps onto the neck of a guitar and shortens the length of the strings, allowing the guitarist to play in different keys without having to learn new chords. An amp is an electronic device that amplifies the sound of the guitar, making it louder. Lastly, a STRAP is a piece of material that attaches to the guitar and allows the guitarist to wear it on their body while playing.