What is "ghost imaging"

n. (context computing English) the process of creating a ghost image of all the contents of a hard drive as a backup that may be stored and later retrieved if needed

Ghost imaging (also called "coincidence imaging") is a technique that produces an image of an object by combining information from two light detectors: a conventional, multi- pixel detector that doesn't view the object, and single-pixel (bucket) detector that does view the object. Whether or not this technique requires quantum entanglement of photons for explanation is debated.