Reference characteristics are characteristics that refer to table fields.
When you classify an object, reference characteristics are not usually available for entry, because the value is taken from the object table and displayed. This ensures that the characteristic values are consistent. If a reference characteristic is used in a class and the reference is to another object type that is different than the current classified object then this object loses its status as a reference characteristic. This means that you can assign a value to the characteristic. You can also use the value you assign to find the classified object.
Example of referance characterstic can be a characterstic refering to PLANT in side of sales order item , you created a characterstic refering to sales order table VBAP field WERKS.
once the sales order number is generated at the time of saving order, this value for plant will be captured as value for this referance characterstic.
and this characterstic can be used to setup or claculating values in some dependencies like procedure.