Entanglement is a physical phenomenon that occurs when two or more particles become connected in such a way that their quantum states are correlated, making it impossible to describe one particle's state independently of the other. This relationship between particles persists regardless of the distance separating them and has been demonstrated experimentally using photons, electrons, and atoms. The concept of entanglement is central to quantum mechanics and plays a key role in many advanced technologies such as quantum computing, quantum cryptography, and quantum teleportation.