Customer. This term means any person who uses a futures commission merchant, introducing broker, commodity trading advisor, or commodity pool operator as an agent in connection with trading in any commodity interest; Provided, however, an owner or holder of a proprietary account as defined in this section shall not be deemed to be a customer within the meaning of section 4d of the Act, the regulations that implement sections 4d and 4f of the Act and 1.35, and such an owner or holder of such a proprietary account shall otherwise be deemed to be a customer within the meaning of the Act and 1.37 and 1.46 and all other sections of these rules, regulations, and orders which do not implement sections 4d and 4f of the Act.
17 CFR § 1.3
Words used in the singular form in the rules and regulations in this chapter shall be deemed to import the plural and vice versa, as the context may require. The following terms, as used in the Commodity Exchange Act, or in the rules and regulations in this chapter, shall have the meanings hereby assigned to them, unless the context otherwise requires: