A Joomla custom field stores an additional structured value on an article or another supported record. Examples include an event date or a product specification.
Type and scope
The field type controls input and validation, such as text, list or calendar values. Joomla fields belong to a component context, can be restricted to categories and can be organised into groups. Support depends on the extension.
Storage and output
Creating a field does not guarantee its desired page position. Joomla settings, plugins and layouts control presentation. Check labels, language, access and empty values. Developer form fields and content custom fields are related but distinct concepts.
Use Joomla custom fields for repeatable structured data rather than manually copying the same specifications into every record’s text.