The distinction between terror and horror was first characterized by the Gothic writer Ann Radcliffe (1764 1823), horror being more related to being shocked or scared (being horrified) at an awful realization or a deeply unpleasant occurrence, while terror is more related to being anxious or fearful.
Linda Bayer-Berenbaum: Both involve fear and repulsion, but terror is more immediate, more emotional, and less intellectual. You may be horrified by what your friend tells you but terrified by what you see yourself. . . . Terror is more potent and stimulating and thus the more Gothic emotion.