The meaning of Astigmatism

Simply put, in the case of an Astigmatism, the front part of the eye (cornea) doesn't have the shape of a ball but the shape of a rugby ball. 

Astigmatism-Meaning-Middle-East

The most important task of the front part of the eye is to focus the incoming light on a spot on the retina, the light sensitive area in the back of the eye.

In case of an Astigmatism, the incoming light gets not focussed properly and therefore causes blurry vision.