just check it up from dict.
1 : a defect of an optical system (as a lens) causing rays from a point to
fail to meet in a focal point resulting in a blurred and imperfect image
2 : a defect of vision due to astigmatism of the refractive system of the eye
and especially to corneal irregularity
3 : distorted understanding suggestive of the blurred vision of an astigmatic
person
