Almost everyday you see a 404 error or Not found message while surfing the Internet. This error occurs when your computer is not able to communicate with a server or server can't find what was requested. Since the decimal form of April 4 coincides with 404, this day has become 404 Day.
The UN General Assembly declared that April 4 is an annual observation of International Day of Landmine and Assistance. This International Day was created in 2005 and its first observation took place in 2006.
World Rat Day is an annual international holiday observed on April 4. It's an unofficial celebration dedicated to fancy rats who are among the most popular pets. The holiday was created in 2002.