Einstein-Podolsky-Rosen effect; EPR effect:
Assume the following quantum mechanical thought-experiment: Take a particle that is at rest and contain spin zero. It decays spontaneously in two fermions (spin 1/2 particles), which stream away into opposite directions at high speed. Because of the law of conservation of spin, we know that one is a spin +1/2 and the other is -1/2. Which one is which? According to quantum mechanics, neither takes on a specific state till it is observed (the wavefunction is collapsed).
The EPR effect revel that if one of the particles is detected, and then its spin is measured, then the other particle no matter where this is in the Universe immediately is forced to select as well and take on the role of the other particle. This demonstrated that certain kinds of quantum information instantaneously travel; not everything is restricted by the speed of light.
But, it can be demonstrated easily that this effect does not make faster-than-light communication or travel possible.