Anti-time
From Memory Alpha, the free Star Trek reference.
Anti-time is a concept in temporal mechanics, relatively new in 2370. The relationship between normal time and anti-time is analogous to the one between matter and antimatter. When time and anti-time interact, the two annihilate each other. This interaction also causes disruptions in space. Because of the nature of anti-time, this disruption - an anti-time eruption - essentially runs "backwards" through time.
Such a disruption was formed in an alternate 2364, 2370 and an unknown future date, as the result of the convergence of three inverse tachyon pulses - one in each time period - which ruptured the subspace barrier. The barrier was later sealed and the disruption, and thus the timeline, eliminated.
Temporal energy resulting from anti-time distortions has unusual effects on organic tissue, which essentially causes it to revert to an earlier stage. This can result in old scars healing themselves or fetal tissue breaking down. (TNG: "All Good Things...")
