415 ILCS 5/3.363

"Prevention of Significant Deterioration permit" or "PSD permit" means a permit or the portion of a permit for a new major source or major modification that is issued by the Illinois Environmental Protection Agency under the construction permit program pursuant to subsection (c) of Section 9.1 that has been approved by the United States Environmental Protection Agency and incorporated into the Illinois State Implementation Plan to implement the requirements of Section 165 of the Clean Air Act and 40 CFR 51.166.