A crystalline domain usually limited by well-defined boundaries.
Polymer crystals frequently do not display the perfection that is usual for low-molar-mass substances.
Twinned polymer crystals are, sometimes, erroneously referred to as 'crystals'.
Polymer crystals that can be manipulated individually are often called (polymer) single crystals. A single crystal may contain different fold domains.
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351/goldbook