One of several species (or @M03986@) that have the same atomic composition (@M03987@) but different @L03561@ or different @S05974@ and hence different physical and/or chemical properties.
Sources: PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1129 [Terms] [Paper] PAC, 1996, 68, 2193. (Basic terminology of stereochemistry (IUPAC Recommendations 1996)) on page 2210 [Terms] [Paper]