A hypothetical line on the Earth running from the North to South Pole generally following the 180° meridian, measured from Greenwich. It divides neighbouring regions so that the date differs by one day.
longitude 180 east and west. The location on the Earth where the date and day change.
A line drawn almost parallel to the 180 degree longitude meridian that marks the location where each day officially begins. The location of the International Date Line was decided upon by international agreement.