The international date line is defined as an imaginary line that goes north and south through the Pacific Ocean, one day is on the east side of the line and the following day is on the west side.
(noun)An example of the international date line is when it's 3pm on Sunday in Samoa, it's 3pm on Monday right across the line, just 550 miles away in Tonga.
See international date line in Webster's New World College Dictionary
See international date line in American Heritage Dictionary 4
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