(a) DeterminationFor purposes of this part, the term “determination” means—
a decision by the Tax Court or a judgment, decree, or other order by any court of competent jurisdiction, which has become final;
(3) a final disposition by the Secretary of a claim for refund. For purposes of this part, a claim for refund shall be deemed finally disposed of by the Secretary—
as to items with respect to which the claim was allowed, on the date of allowance of refund or credit or on the date of mailing notice of disallowance (by reason of offsetting items) of the claim for refund, and
Notwithstanding section 7701(a)(14), the term “taxpayer” means any person subject to a tax under the applicable revenue law.
(c) Related taxpayerFor purposes of this part, the term “related taxpayer” means a taxpayer who, with the taxpayer with respect to whom a determination is made, stood, in the taxable year with respect to which the erroneous inclusion, exclusion, omission, allowance, or disallowance was made, in one of the following relationships:
member of an affiliated group of corporations (as defined in section 1504).