International Date Line

A line, falling near 180 degrees West (or East) longitude, where each day begins. In other words, a new day officially begins when the local time along the International Date Line is midnight.

Although the International Date Line runs North and South, it is not a line of longitude. That's because the date line zigs and zags to avoid populated areas of the Pacific Ocean, in order to avoiding having a single population divided by the line.

Contrast with Prime Meridian