Meaning of ZONE in English
(n.) In the United States parcel-post system, any of the areas about any point of shipment for which but one rate of postage is charged for a parcel post shipment from that point. The rate increases from within outwards. The first zone includes the unit of area "(a quadrangle 30 minutes square)" in which the place of shipment is situated and the 8 contiguous units; the outer limits of the second to the seventh zones, respectively, are approximately 150, 300, 600, 1000, 1400, and 1800 miles from the point of shipment; the eighth zone includes all units of area outside the seventh zone.
Webster's English dictionary. Английский словарь Webster. 2012