Haikomei (name for men representing the order of their birth) (輩行名)

A haikomei is a type of name for men used mostly in Japan. Haikomei has also been called "haiko no kemyo" and "haiko kemyo." Before the Edo period, it was a kind of kemyo (assumed name).

The meaning of Haikomei
"Haiko" carries the meaning of "people of the same generation within a family," typically in the case of brothers. Haikomei represents the seniority in the "Haiko" (birth order) in names such as Taro, Jiro and Saburo, and they are widely used as given names today. Often one character is added in front of the names, "Taro, Jiro" and so forth.

The origin of such names as Taro and Jiro goes all the way back to the time of Emperor Saga. As Emperor Saga gave the childhood name Taro to the first prince, Jiro to the second prince, Saburo to the third prince and so forth, these names spread to the general populace over time. In the samurai (warrior) class in particular, Haikomei had already spread in the Heian period, as seen by examples such as the legitimate son of MINAMOTO no Yoriyoshi taking the name MINAMOTO no Yoshiie and his younger brothers taking the names MINAMOTO no Yoshitsuna and MINAMOTO no Yoshimitsu. Over time, names such as Taro and Jiro were widely used in both the samurai and merchant classes. Haikomei used by the samurai class were assumed names, while in the merchant class they were real names due to merchants not having an imina (personal name).

Names such as Taro and Jiro do no always correspond to the order in which they are born. For example, although Hideie UKITA was a second son, his childhood name was "Hachiro" (meaning the "eighth" son), and in other cases, a predecessor's name was handed down, as seen in the case of Shirojiro CHAYA.
(In fact, "Shirojiro" means "the second son of Shiro.")