The eight-character birthday is a person's date of birth. These eight words have a place in Chinese folk beliefs. The stems and branches of a year form a column of years, the stems and branches of a month form a column of months, the stems and branches of a day form a column of days, and the stems and branches of a year form a column of times. A total of four pillars, four stems and four branches, a total of eight words, so it is also called four pillars and eight characters.