220 ILCS 5/3-121
As used in Section 2-202 of this Act, the term "gross revenue" includes all revenue which (1) is collected by a public utility subject to regulations under this Act (a) pursuant to the rates, other charges, and classifications which it is required to file under Section 9-102 of this Act and (b) pursuant to emergency rates as permitted by Section 9-104 of this Act, and (2) is derived from the intrastate public utility business of such a utility. Such term does not include revenue derived by such a public utility from the sale of public utility services, products or commodities to another public utility, to an electric cooperative, or to a natural gas cooperative for resale by such public utility, electric cooperative, or natural gas cooperative. "Gross revenue" shall not include any charges added to customers' bills pursuant to the provisions of Section 9-221, 9-221.1 and 9-222 of this Act or consideration received from business enterprises certified under Section 9-222.1 of this Act to the extent of such exemption and during the period in which the exemption is in effect.
220 ILCS 5/3-121