The term 'Instrument with Keys' can refer to three different instruments: the PIANO (5 letters), the ORGAN (5 letters), and the OBOE (4 letters). The PIANO is a stringed instrument that produces sound when its keys are pressed. It is one of the most popular instruments in the world and is used in many genres of music. The ORGAN is a keyboard instrument that produces sound by air being pushed through pipes. It is commonly used in churches and other religious settings. The OBOE is a woodwind instrument that produces sound when its keys are pressed. It is often used in orchestras and other classical music settings.