January 1 represents the fresh start of a new year after a period of remembrance of the passing year. This day is traditionally a religious feast, but since the 1900s has also become an occasion to celebrate the night of December 31, called New Year's Eve.
New Year's Day is the closest thing to being the world's only truly global public holiday, often celebrated with fireworks at the stroke of midnight as the New Year starts with most countries using the Gregorian calendar as their main calendar.
New Year's Day is observed on January 1, the first day of the year on the modern Gregorian calendar as well as the Julian calendar used in ancient Rome.
The Romans dedicated New Year's Day to Janus, the god of gates, doors, and beginnings for whom the first month of the year (January) is also named. Most countries in Western Europe officially adopted January 1 as New Year's Day somewhat before they adopted the Gregorian calendar.