The theremin is an electronic musical instrument invented in the 1920s by Leon Theremin. It is unique because it is played without physical contact; musicians control pitch and volume by moving their hands near two metal antennas. The closer the hands are to the antennas, the higher the pitch or louder the sound. The sound produced by the theremin is often described as eerie or otherworldly, making it popular in film scores, especially in the science fiction genre. Its distinctive tones have been used in various music styles, from classical to rock, showcasing its versatility and unique sound.