Extensible Flexfield attributes are custom attributes that you can add to Order Management entities to capture additional information that is specific to your business needs. You can use these attributes in approval rules for sales orders to define conditions and actions based on the values of the attributes. The order entities that support the use of Extensible Flexfield attributes in approval rules for sales orders are Header, Line, and Fulfillment Line. These entities have predefined Extensible Flexfield categories that you can configure and deploy in the Setup and Maintenance work area. You can also access and update these attributes in the Order Management work area.
Reference:
Overview of Using Extensible Flexfields in Order Management
Set Up Extensible Flexfields in Order Management
Oracle Order Management Cloud - Extensions