己卯 is formed by combining the character 己, which is the sixth of the ten Heavenly Stems, with the character 卯, which is the fourth of the twelve Earthly Branches, in a fixed sequential order from the traditional Chinese cyclical system. This pairing results in one of the 60 designated terms used for marking years, months, days, and times, with each character serving as a standardized symbol within this calendrical framework.