The type of discount or "rule" that is being used by the profile. The value corresponding to the selected rule is set in the same-named field of FlatShippingDiscount.DiscountProfile. All are "variable" rules, as defined in the documentation on shipping discount profiles.
See the Field Index to learn which calls use DiscountName.
Details of this particular flat rate shipping discount profile. If ModifyActionCode is Modify, all details of the new version of the profile must be provided. If ModifyActionCode is Delete, DiscountProfileID is required, MappingDiscountProfileID is optional, and all other fields of DiscountProfile are ignored. Restrictions of how many profiles you can have for a given discount rule are discussed in the documentation on shipping discount profiles.
See the Field Index to learn which calls use DiscountProfile.