Actually, it is in the name and pretty simple. It is surprisingly called the International Date Line
The international Date Line.
Because when you cross it, you must change your calendar by one day, otherwise you will be out of sync with everyone else in the world.
the international date line
Midnight.
false
Slope. I'm pretty sure.
the whole world agrees that the date changes on each side of the line
It is along 180 degrees longitude, but it doesn't run in a straight line.
The 180th meridian is also called the International Date Line because that is where the day changes from one day to the next. Keep in mind that the date change does not follow exactly the 180th meridian and moves slightly east or west as necessary to accommodate the desires of the various countries that lie along it.
The International Date Line runs roughly along the 180° longitude, (opposite the Prime Meridian), but it is drawn with diversions to pass around some territories and islands.
International Date Line
The line 180 degrees from the Prime Meridian is called the International Date Line, which serves as the boundary between one day and the next on the Earth's surface.