Aberration (Lat. ab, from or away, errare, to wander), a deviation or wandering, especially used in the figurative sense: as in ethics, a deviation from the truth; in pathology, a mental derangement; in zoology and botany, abnormal development or structure. In optics, the word has two special applications: (1) Aberration of light, and (2) Aberration in optical systems. These subjects receive treatment below.