Explanation:

• International Date Line, also called Date Line, an imaginary line extending between the North Pole and the South Pole and arbitrarily demarcating each calendar day from the next. It corresponds along most of its length to the 180th meridian of longitude but deviates eastward through the Bering Strait to avoid dividing Siberia and then deviates westward to include the Aleutian Islands with Alaska. South of the Equator, another eastward deviation allows certain island groups to have the same day as New Zealand. It is not a straight line, but a zig-zag line.
• On crossing it from east to west, a day is lost. Like if a traveller starts from Kyoto (Japan) towards California (America) on 1st January 2019, on crossing International Date Line the date will be 31st December 2018. Similarly, on crossing it from west to east, a day is gained.