26 CFR § 31.3406(h)-1 - Definitions.
(a) In general. For purposes of section 3406 and the regulations thereunder, the definitions of this section apply.
(b) Taxpayer identification number—(1) In general. Taxpayer identification number means the identifying number assigned to a person under section 6109 (relating to identifying numbers, generally a nine-digit social security number for an individual and a nine-digit employer identification number for a nonindividual, e.g., a corporation, partnership, trust, or estate). An obviously incorrect number is not considered a taxpayer identification number. See § 31.6011(b)–2 and § 301.6109–1 of this chapter for provisions relating to obtaining a taxpayer identification number.
(2) Obviously incorrect number. Obviously incorrect number means a number that does not contain nine digits or a number that includes an alpha character as one of the nine digits.
(c) Broker. Broker is defined in section 6045(c)(1) and § 1.6045–1(a)(1) of this chapter. If there could be more than one broker with respect to any acquisition, only the broker having the closest contact (as determined under 1.6045–1(c)(3)(iii) and (iv) of this chapter) with the payee is treated as a broker. In the case of any instrument, the term broker does not include any person who is the payor with respect to the instrument as described in § 31.3406(a)–2.
(d) Readily tradable instrument. Readily tradable instrument means—
(1) Any instrument that is part of an issue any portion of which is traded on an established securities market (within the meaning of section 453(f)(5)); or
(2) Any instrument that is regularly quoted by brokers or dealers making a market.
(f) Business day. Business day means any day other than a Saturday, Sunday, or legal holiday (within the meaning of section 7503).