A qubit, or quantum bit, is the fundamental unit of quantum information, analogous to a classical bit in traditional computing. Unlike a classical bit, which can be either 0 or 1, a qubit can exist in a state of superposition, meaning it can be both 0 and 1 simultaneously. This unique property allows quantum computers to process vast amounts of information more efficiently than classical computers. Qubits can be realized using various physical systems, such as trapped ions, superconducting circuits, or photons. The ability to entangle qubits further enhances their computational power, enabling complex calculations that are currently infeasible for classical systems.