FRM
Federal reference method (FRM) means a method of sampling and analyzing the ambient air for an air pollutant that is specified as a reference method in an appendix to part 50 of this chapter, or a method that has been designated as a reference method in accordance with this part; it does not include a method for which a reference method designation has been canceled in accordance with 53.11 or 53.16 of this chapter.
Source
40 CFR § 58.1
Scoping language
As used in this part, all terms not defined herein have the meaning given them in the Clean Air Act.