A zi (字 pinyin: zi4), translated sometimes as style or courtesy name, is a pseudonym used by an educated Chinese before modern time and is no longer in fashion today. It was usually chosen at the age of 20 and based on the meaning of the given name. Prior to the 20th century, Sinicized Koreans and Japanese also used zi. In Korean, it is translated as cha (자). In Japanese, it is translated as azana or ji.
The relation between the zi and given name is evident in the case of Mao Zedong, but not all. One character from each of Mao's given name and zi is related to water (as evident by the characters' common radical 氵 that signifies "water") and beneficence: Ze (澤 ze2) of the given name Zedong means "beneficence" and "marsh", and Run (润 run4) of the zi Runzhi means "benefit" and "moisten".
Zi and birth given name cannot be used in consecution like given and middle names are. A stranger would refer to the person by his/her Zi rather than given name. For the same reason, Zi is used in writing instead of given name. Zi did not include the family name.