A synchronic distortion, also known as a phase differential, was a phenomenon whereby an object or person existed in a different time continuum.
In the 24th century, the Devidians used a synchronic distortion with a positive displacement of .004 percent. This made them invisible to the crew of the USS Enterprise-D, who arrived at Devidia II to investigate the Devidians' temporal incursions to 19th century Earth. By utilizing a subspace force field and a phase discriminator, they were able to enter the Devidians' continuum, and follow them through the temporal vortex they were using to travel through time.
Later, by outfitting them with phase discriminators, Geordi La Forge was able to program several photon torpedoes to phase-shift into the Devidians' continuum, enabling the Enterprise-D to destroy their habitat from orbit. (TNG: "Time's Arrow", "Time's Arrow, Part II")