Superposition is a fundamental principle in quantum mechanics that states a quantum system can exist in multiple states at once until it is measured. This means that particles, like electrons, can be in different positions or energy levels simultaneously, leading to phenomena such as interference patterns in experiments. In classical physics, superposition refers to the ability of waves to overlap and combine, resulting in a new wave pattern. This principle is crucial in understanding sound waves and light waves, where multiple waves can coexist and interact, creating complex behaviors in various physical systems.