31 CFR §566.309

1. (a)The term foreign financial institution means:
   1. (1)A foreign bank;
   2. (2)Any branch or office located outside the United States of a covered financial institution, as defined in § 566.303;
   3. (3)Any other person organized under foreign law (other than a branch or office of such person in the United States) that, if it were located in the United States, would be a covered financial institution, as defined in § 566.303; and
   4. (4)Any person organized under foreign law (other than a branch or office of such person in the United States) that is engaged in the business of, and is readily identifiable as, a dealer in foreign exchange or a money transmitter.
2. (b)For purposes of paragraph (a)(4) of this section, a person is not “engaged in the business” of a dealer in foreign exchange or a money transmitter if such transactions are merely incidental to the person's business.