Oxford English Dictionary:
1. a. A kind of decorative painting or sculpture, consisting of representations of portions of human and animal forms, fantastically combined and interwoven with foliage and flowers.
b. A work of art in this style. Chiefly pl., figures or designs in grotesque; in popular language, figures or designs characterized by comic distortion or exaggeration. The Italian form grottesco (pl. grotteschi) is sometimes used.
from Wikipedia: the strange, fantastic, ugly, incongruous, unpleasant, or disgusting . . . often used to describe weird shapes and distorted forms. In art, performance, and literature, grotesque may also simultaneously invoke in an audience a feeling of uncomfortable bizarreness and empathic pity. (Compare / contrast catharsis)
Hieronymus Bosch, Christ Carrying the Cross (1490)
Metsys, A Grotesque Old Woman