Horror isn't an element only in movies or literature. Artists throughout the time have painted many repulsive and ghastly themes. For example, an elderly man is devouring his own son, a beautiful lady is beheading her enemy, and a sculpture of a faceless head is pouring a thick, black fluid.
Alternatively, horror can be considered an art that forms an unease in the viewer and strikes as a temptation in a very unusual way. While horror could appear grotesque and gory most of the time, it could also be sublime and subdued.