Section 205.165 - Definitions(a) As used in this subpart, all terms not defined herein have the meaning given them in subpart D of this part or in the Act.(1)Category means a group of exhaust systems which are identical in all material aspects with respect to the parameters listed in § 205.168 of this subpart.(2)Exhaust header pipe means any tube of constant diameter which conducts exhaust gas from an engine exhaust port to other exhaust system components which provide noise attenuation. Tubes with cross connections or internal baffling are not considered to be "exhaust header pipes."(3)Failing exhaust system means that, when installed on any Federally regulated motorcycle for which it is designed and marketed, that motorcycle and exhaust system exceed the applicable standards.(4)Federally regulated motorcycle means, for the purpose of this subpart, any motorcyle subject to the noise standards of subpart D of this part.(5)Federal standards means, for the purpose of this subpart, the standards specified in § 205.152(a)(1), (2) and (3) .(7)Stock configuration means that no modifications have been made to the orginal equipment motorcycle that would affect the noise emissions of the vehicle when measured according to the acceleration test procedure.(8)Test exhaust system means an exhaust system in Selective Enforcement Audit test sample.45 FR 86718, Dec. 31, 1980, as amended at 47 FR 57722, Dec. 28, 1982