configurational base unit

in polymers
A constitutional repeating unit in a regular macromolecule, a regular oligomer molecule, regular block or a regular chain, the configuration of which is defined at least at one site of stereoisomerism in the main chain (backbone).
PAC, 1996, 68, 2287. 'Glossary of basic terms in polymer science (IUPAC Recommendations 1996)' on page 2291 (