Model year
Model year means the manufacturer's annual new model production period which includes January 1 of the calendar year for which the model year is named, ends no later than December 31 of the calendar year, and does not begin earlier than January 2 of the previous calendar year. Where a manufacturer has no annual new model production period, model year means the calendar year.
Source
40 CFR § 91.3
Scoping language
The following definitions apply to this part 91. All terms not defined herein have the meaning given them in the Act.