Friday the 13th, also known as Black Friday in some countries, is considered an unlucky day in Western superstition. It occurs when the 13th day of the month in the Gregorian calendar falls on a Friday. There is no written evidence for a "Friday the 13th" superstition before the 19th century, and the superstition only gained widespread distribution in the 20th century. The fear of the number 13 has been given a scientific name: triskadekaphobia; and on analogy to this the fear of Friday the 13th is called paraskevidekatriaphobia, from the Greek words Paraskeví (Παρασκευή, meaning "Friday"), anddekatreís (δεκατρείς, meaning "thirteen").
It's not known for certain how the superstition surrounding this day arose, but both Friday and the number 13 are connected with the crucifixion of Christ (Friday being the day the crucifixion took place, commemorated weekly in Catholic practice, and 13 being the number of people present at the Last supper). According to Phillips Stevens, Jr., associate professor of anthropology at theUniversity at Buffalo (SUNY), "There were 13 people at the table (at the Last Supper) and the 13th was Judas. The Last Supper was on a Thursday, and the next day was Friday, the day ofcrucifixion. When '13' and Friday come together, it is a double whammy."
Friday has been considered an unlucky day to undertake journeys or begin new projects at least since the 14th century, as witnessed by Chaucer's Canterbury Tales.
However, folklorists maintain that there is no written evidence for a "Friday the 13th" superstition before the 19th century. An early documented reference in English occurs in Henry Sutherland Edwards' 1869 biography of Gioachino Rossini, who died on a Friday 13th.