What is the best-selling single worldwide?

Context: According to Guinness World Records, Irving Berlin's "White Christmas" as performed by Bing Crosby is the best-selling single worldwide, with estimated sales of over 50 million copies. The song, recognized as "the best-selling single of all time", was released before the pop/rock singles-chart era and "was listed as the world's best-selling single in the first-ever Guinness Book of Records and—remarkably—still retains the title more than 50 years later".

Answer: The best-selling single worldwide, according to Guinness World Records, is Irving Berlin's "White Christmas", which was performed by Bing Crosby in 1942 with over 50 million copies sold.