In the context of physics, particularly quantum mechanics, a "hidden variable" refers to an unobservable property or parameter that deterministically influences the outcomes of quantum measurements. The term is often associated with theories that attempt to explain the seemingly random behavior of quantum systems by positing that there are underlying factors we cannot measure or observe directly. In quantum mechanics, the outcomes of measurements are fundamentally probabilistic, as described by the wave function and governed by the principles of superposition and entanglement.