Refractive error. Astigmatism is a measure of how "unround" the eye is. We tend to think that the eye is a perfectly round globe, but it actually is almost always at least a little oblong, like a rugby ball. The degree to which the front window (cornea) is oblong is measured in amount and angle of astigmatism (in which direction the ball is standing). Glaucoma has nothing to do with astigmatism.
Different things. Astigmatism is a refractive error of the eye, typically either from the cornea or lens. It is typically corrected with either glasses or contacts. This is different from glaucoma. However, glaucoma and astigmatism can occur at the same time, especially after glaucoma surgery where incisions on the eye can change astigmatism.