A cloaking device which (roughly as defined in Star Trek: The Next Generation) alters the phase-state of the matter of the cloaked starship allowing it to pass through normal matter. The USS Pegasus was lost when conducting experiments with a Phasing Cloak, and later discovered in the episode The Pegasus. The term Phasing Cloak has appeared in other sci-fi settings, and the idea behind it seems to be at least somewhat consistent, from what I can see.