Chirality is an important geometric property relating to a molecule's symmetry. A chiral molecule is non-superimposable with its mirror image, and has a "handedness" (think of shoes, which specifically go with a right or left foot). An achiral molecule is superimposable with its mirror image and do not have "handedness" (think of a baseball bat, which can be used with either hand).
License: CC BY-NC-SA by Khan Academy