Term: fold domain https://doi.org/10.1351/goldbook.F02474 Definition: A portion of a polymer crystal wherein the fold planes have the same orientation. The sectors of lamellar crystals frequently represent fold domains. Related Terms: 1) polymer crystal (http://doi.org/10.1351/goldbook.P04737). Source: Purple Book, 1st ed., p. 83 (http://old.iupac.org/publications/books/author/metanomski.html) Citation: 'fold domain' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.F02474 License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms. Disclaimer: The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.