A temporal causality loop is a special condition of time, in which time runs for a certain period, then resets itself to a point back in time, after which the events play out over again. However, afterimages of previous loops can be found to have effect on the dekyon field. This causes humanoid lifeforms to experience deja-vu's.
A causality loop can be caused by an antimatter explosion in close proximity to a temporal anomaly. The USS Bozeman and the USS Enterprise-D were caught in a causality loop after they collided near a temporal anomaly in the Typhon Expanse. (TNG: "Cause and Effect")