Quantum entanglement is a property of the quantum mechanical state of a system containing two or more objects, where the objects that make up the system are linked in such a way that the quantum state of any of them cannot be adequately described without full mention of the others, even if the individual objects are spatially separated. Quantum entanglement is at the heart of the EPR paradox described by Albert Einstein, Boris Podolsky and Nathan Rosen in 1935, and was verified experimentally for the first time in 1972 by Stuart Freedman and John Clauser.

http://en.wikipedia.org/wiki/Quantum_Entanglement