Wave–particle duality is a fundamental principle in quantum mechanics proposing that all matter and energy exhibit properties of both waves and discrete particles. According to this concept, entities such as photons and electrons do not behave strictly as one or the other, but rather possess characteristics of both. When measured under certain conditions, a quantum entity may display wave behavior, such as exhibiting interference patterns, which is associated with the spreading nature of waves. Conversely, when detected or measured in interaction, the entity behaves as a localized particle, possessing discrete amounts of momentum and energy. This dual nature is essential for understanding the behavior of matter at the atomic scale, demonstrating that classical descriptions of reality are incomplete and necessitating a quantum description involving both wave functions and particulate interactions.