The ability to bring two particular
stereochemical formulae (or models) into coincidence (or to be exactly superposable in space, and for the
corresponding molecular entities or objects to become exact replicas of each other)
by no more than translation and rigid rotation.
Source:
PAC, 1996, 68, 2193
(Basic terminology of stereochemistry (IUPAC Recommendations 1996))
on page 2220