31 C.F.R. § 515.327

The term blocked estate of a decedent shall mean any decedent's estate in which a designated national has an interest. A person shall be deemed to have an interest in a decedent's estate if he:

(a) Was the decedent;

(b) Is a personal representative; or

(c) Is a creditor, heir, legatee, devisee, distributee, or beneficiary.