Courtesy name

A courtesy name (), also known as a style name, is a name bestowed upon one at adulthood in addition to one's given name. This practice is a tradition in the Sinosphere, including China, Japan, Korea, and Vietnam.
The courtesy name would replace a man's given name as he entered adulthood. It could be given either by the parents or by a private teacher on the first day of school. Women might adopt a "zi" in place of their given name upon marriage. One also may adopt a self-chosen courtesy name.
A courtesy name is not to be confused with an art name ("hào", , Korean: ), another frequently mentioned term for an alternative name in Asian culture-based context. An art name is usually associated with art and is more of a pen name or a pseudonym that is more spontaneous, compared to a courtesy name.
Usage.
The "zì", sometimes called the "biǎozì" () or "courtesy name", is a name traditionally given to Chinese men at the age of 20, marking their coming of age. It was sometimes given to women upon marriage. The practice is no longer common in modern Chinese society. According to the "Book of Rites", after a man reaches adulthood, it is disrespectful for others of the same generation to address him by his given name, or "míng". Thus, the given name was reserved for oneself and one's elders, whereas the zì would be used by adults of the same generation to refer to one another on formal occasions or in writing; hence the term "courtesy name".
The "zì" is mostly disyllabic, consisting of two Chinese characters, and is often based on the meaning of the "míng" or given name. For example, Chiang Kai-shek's "zì" (, romanized as Kai-shek) and "ming" (, romanized as Chung-cheng) are both from the "yù" hexagram of I Ching. 
Yan Zhitui of the Northern Qi dynasty asserted that whereas the purpose of the "míng" was to distinguish one person from another, the "zì" should express the bearer's moral integrity.
Another way to form a "zì" is to use the homophonic character "zǐ" () – a respectful title for a man – as the first character of the disyllabic "zì". Thus, for example, Gongsun Qiao's "zì" was Zǐchǎn (), and Du Fu's: Zǐměi ().
It is also common to construct a "zì" by using as the first character one which expresses the bearer's birth order among male siblings in his family. Thus Confucius, whose name was Kǒng Qiū (), was given the "zì" Zhòngní (), where the first character "zhòng" indicates that he was the second son born into his family. The characters commonly used are bó () for the first, zhòng () for the second, shū () for the third, and jì () typically for the youngest, if the family consists of more than three sons. General Sun Jian's four sons, for instance, were Sun Ce (, Bófú), Sun Quan (, Zhòngmóu), Sun Yi (, Shūbì) and Sun Kuang (, Jìzuǒ).
The use of "zì" began during the Shang dynasty, and slowly developed into a system which became most widespread during the succeeding Zhou dynasty. During this period, women were also given "zì". The "zì" given to a woman was generally composed of a character indicating her birth order among female siblings and her surname. For example, Mèng Jiāng () was the eldest daughter in the Jiāng family.
Prior to the twentieth century, sinicized Koreans, Vietnamese, and Japanese were also referred to by their "zì". The practice was also adopted by some Mongols and Manchus after the Qing conquest of China.