Chirality

Chirality refers to a molecule or object that cannot be superimposed, rotated an amount of degree, to match its mirror immage.

For instance your right and left hand are mirror images of each other. Hands are chiral:

There is no way to rotate your left hand so it matches perfectly on top of your right hand.

A chair is non chiral. You can rotate it in such a way that it would like up to its mirror image.