"Harmonic" refers to a concept in music and physics that relates to the frequencies of sound waves. In music, harmonics are the overtones produced when a note is played, creating a richer sound. For example, when a guitar string vibrates, it produces a fundamental frequency along with higher frequencies called harmonics, which contribute to the instrument's unique tone. In physics, harmonic motion describes a repetitive movement, such as a swinging pendulum or a vibrating spring. This type of motion can be mathematically modeled using sine and cosine functions, illustrating how systems oscillate around an equilibrium point. Harmonic concepts are essential in fields like acoustics, engineering, and music theory.