What is international dateline west?

The International Date Line (IDL) is an imaginary line located at approximately 180 degrees longitude, opposite the Prime Meridian. The west side of the IDL is where the time is one day earlier compared to the east side. When crossing the IDL from east to west, travelers add a day to their calendar, while crossing from west to east subtracts a day. The line allows for a standardized transition between days and is crucial for global timekeeping.