Precondition: Custom fields have been defined…
Field names configuration
...
The dropdown for the Default name will list all custom fields generally available on the Jira instance. The list includes the custom field type. A hint “not on any screens” will be displayed if the field is actually not usable for you since it is not (yet) configured for any issue screens of your project. Select the field for which you would like to define a custom name (and description).
The Default description shows the globally configured descripion for the field (either directly for the custom field or via the field configuration scheme).
Enter a custom name and, if you would like to, a custom description for the field. This name and description will replace the default name and description on the user-facing screens of your project (see also https://bitperium.atlassian.net/wiki/spaces/JPSFN/overview, chapter “Scope of our app”.
Hit Save.
...