International Date Line
The International Date Line (IDL) is an imaginary line on the Earth's surface located at about 180 degrees longitude, opposite the Prime Meridian. It is the line where one day changes to the next. When you cross the International Date Line from west to east, you subtract a day, and when you cross from east to west, you add a day.

Significance
The International Date Line is important for keeping time consistent around the world. It ensures that when it is daytime on one side of the line, it is nighttime on the other side. This helps in coordinating international travel, communication, and commerce.

Impacts
The International Date Line has some interesting impacts on geography and time. For example, the small islands of Samoa and Tokelau decided to switch sides of the date line in 2011 to align themselves with their major trading partners in Australia and New Zealand. This resulted in Samoa skipping a day and moving straight to the next day.

Changes over time
The International Date Line has been adjusted several times in history to accommodate political and economic needs. For example, the line used to zigzag around certain territories to ensure they fell under the same day. However, in 1995, the line was straightened out to simplify things.
In conclusion, the International Date Line plays a crucial role in maintaining a standardized system of timekeeping across the globe. It may seem like an imaginary concept, but its impact on international relations and commerce is very real.