Zone-of- Reasonableness -A zone or limit within which air carriers are permitted to change rates without regulatory scrutiny; if the rate change is within the zone, the new rate is presumed to be reasonable.

Zone-of-Trade Flexibility - Railroads are permitted to raise rates by a percentage increase in the railroad cost index determined by the ICC; rates may be raised by 4 percent.

Zulu Time - Time that is based on Greenwich Mean Time.