A harmonic oscillator is a physical system that undergoes periodic motion because of a restoring force proportional to its displacement from an equilibrium point. Mathematically, this behavior is modeled by simple harmonic motion, where the force acting on the object is described by Hooke's Law. These systems exhibit a predictable natural angular frequency and frequency of oscillation, which depend only on the system's mass and the spring constant or equivalent stiffness of the restoring mechanism. The concept is foundational in wave mechanics, vibrating systems, and quantum physics, providing a simplified yet powerful model for analyzing energy transfer and oscillatory behavior across mechanical, electrical, and molecular domains.