quantum entanglement

Definition: A phenomenon in quantum mechanics in which set of (more than one)particles do not individually have a definite state but exist as an intermediate form of multiple “superposed” states. Each of these states describes each particle in a definite individual state. One of these states is realized when a 'measurement' is made on any one of the particles, placing all the other particles in the corresponding definite states, with out any measurements being directly carried out upon them! This effect (described by Einstein as "spooky action at a distance") was the subject of the "Einstein-Podolsky-Rosen Paradox" that was part of the reason that Albert Einstein did not particlarly like quantum mechanics - despite his role in creating it!