What is biggest hit song?

According to the Guinness World Records, the biggest hit song of all time is "White Christmas" by Bing Crosby. Released in 1942, the song has sold an estimated 50 million copies worldwide, making it the best-selling single of all time. The song was written by Irving Berlin and was featured in the 1942 film "Holiday Inn." It has been recorded by numerous artists over the years, but Bing Crosby's version remains the most popular.