What is "stereoisomerism"

n. (context chemistry English) A form of isomerism in which atoms are arranged differently about a chiral centre (or centre of asymmetry); they exhibit optical activity; in a molecule with a single chiral centre the two isomers (enantiomers) are mirror images of each other; in a molecule with multiple chiral centres the isomers (diastereoisomers) are not normally mirror images.

Stereoisomers are isomeric molecules that have the same molecular formula and sequence of bonded atoms (constitution), but differ in the three-dimensional orientations of their atoms in space. This contrasts with structural isomers, which share the same molecular formula, but the bond connections or their order differs. By definition, molecules that are stereoisomers of each other represent the same structural isomer.