Chirality
The property of a molecule that makes it non-superimposable on its mirror image.
Unit
Dimensionless
In depth
Chirality most commonly arises from a carbon bearing four different groups, called a stereocentre, but any molecule lacking an internal plane or centre of symmetry is chiral. A molecule with n stereocentres can have up to 2ⁿ stereoisomers.
Examples in the real world
Human hands as the everyday analogy; every amino acid except glycine; the helical structure of DNA.