26 CFR 1.643(c)-1: (c)-1 Definition of “beneficiary”.

An heir, legatee, or devisee (including an estate or trust) is a beneficiary. A trust created under a decedent's will is a beneficiary of the decedent's estate. The following persons are treated as beneficiaries:

(a) Any person with respect to an amount used to discharge or satisfy that person's legal obligation as that term is used in § 1.662(a)-4.

(b) The grantor of a trust with respect to an amount applied or distributed for the support of a dependent under the circumstances specified in section 677(b) out of corpus or out of other than income for the taxable year of the trust.

(c) The trustee or cotrustee of a trust with respect to an amount applied or distributed for the support of a dependent under the circumstances specified in section 678(c) out of corpus or out of other than income for the taxable year of the trust.