Isomers that possess identical constitution, but which differ in the arrangement of their atoms in space.
See: cis-trans isomers, diastereoisomer, enantiomer
Source:
PAC, 1996, 68, 2193. 'Basic terminology of stereochemistry (IUPAC Recommendations 1996)' on page 2219 (https://doi.org/10.1351/pac199668122193)