aberration

noun

• a departure from what is normal, usual, or expected, typically one that is unwelcome:they described the outbreak of violence in the area as an aberration
• Biology a characteristic that deviates from the normal type:color aberrations
• Optics the failure of rays to converge at one focus because of limitations or defects in a lens or mirror.
• Astronomy the apparent displacement of a celestial object from its true position, caused by the relative motion of the observer and the object.