Quantum refers to the smallest discrete unit of energy or matter in physics, often associated with the behavior of particles at the atomic and subatomic levels. It is a fundamental concept in quantum mechanics, which studies how these particles interact and behave in ways that differ from classical physics. In the quantum world, particles can exist in multiple states at once, a phenomenon known as superposition. Additionally, quantum entanglement describes how particles can become interconnected, such that the state of one instantly influences the state of another, regardless of the distance separating them.