The Heisenberg compensator was a component of the transporter system. The compensator worked around the problems caused by the Heisenberg Uncertainty Principle, allowing the transporter sensors to compensate for their inability to determine both the position and momentum of the target particles to the same degree of accuracy. This ensured the matter stream remained coherent during transport, and no data was lost.
While trying to devise a way to transport holographic matter off the holodeck without it disintegrating instantly, the idea was put forth that decoupling the Heisenberg compensators might let the matter reform normally, although the suggestion was used as a stalling tactic against Professor James Moriarty, and the idea had never actually been tried before. (TNG: "Ship in a Bottle")