[Personal comment: Not happy with this page - need to improve the layout and give some clear examples. Sara explained the CF in the chat. ]
Besides the TBX fields, you can also configure your own custom fields in your terminology management tool.
Go to Settings and search for Terminology Management.
Click on Use Configure to access the Customization page of Terminology management and TBX.
Go to Access rights > Custom field and click on Configure custom fields.
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For example, let us assume that you would like to create a custom field called Illustration where you can add an image to represent a concept in the terminology database. Further you could grant editing access to your internal users and only viewing rights to your external users.
To be completed