A phenomenon involving a large group of people all incorrectly remembering a past event or fact. The phrase is named for the purportedly widespread misconception that Nelson Mandela died in the 1980s while in prison. (Mandela died in 2013 after having served as president of South Africa from 1994 to 1999 following his release from prison in 1990.) Apparently, the company's name was always spelled that way, so you guys remembering it differently must be the Mandela effect.