Spherical aberration
Coma
Astigmatism
Petzval field curvature
Chromatic aberration
Defocus
Tilt
An optical system with astigmatism is one where rays that propagate in two perpendicular planes have different foci. If an optical system with astigmatism is used to form an image of a cross, the vertical and horizontal lines will be in sharp focus at two different distances. The term comes from the Greek α- (a-) meaning "without" and στίγμα (stigma), "a mark, spot, puncture".
Read more about Astigmatism: Forms of Astigmatism