What are user-defined fields in Sitecore?

User-defined fields in Sitecore refer to custom fields that users can add to Sitecore templates. This capability allows developers and content authors to tailor their content structures according to specific requirements, providing greater flexibility in how data is structured and managed within the Sitecore CMS. By adding custom fields, users can capture unique information that isn't covered by the standard fields provided by Sitecore, thereby enhancing the ability to create rich, customized content types.

In contrast, predefined fields refer to those that come with Sitecore templates out of the box and are not customized by the user. Fields that are automatically generated by Sitecore typically arise from system processes or configurations and do not require user intervention. Finally, fields reserved for system use only are those that are essential for Sitecore's internal operations and should not be modified or used for storing custom content. This distinction highlights the unique role that user-defined fields play in extending Sitecore's functionality to better meet specific business needs.