Heimin (commoners) (平民)
Heimin means ordinary citizens without any official rank or title. They are often compared with kizoku (nobles).
The term heimin designated a class of family and was created in 1869 in Japan. Families other than kuge (court nobles), daimyo-ke (families of feudal lords) and upper-class warrior families were designated as heimin which were ranked below kazoku (nobility class) and shizoku (warrior classes). This designation was annulled in 1947 when the aristocracy system in Japan was abolished.
Any one who was born in a family of kazoku or shizoku but did not succeed the family to set up a new branch was basically classified as heimin despite the designation of his parents' home (for example, Takashi HARA who was called a commoner prime minister became heimin after he was born as a son of the chief retainer of the Morioka domain.)
However, there were cases where some branch families of kazoku were also ranked as kazoku due to special considerations, and a son of a kazoku family who was not an heir of the family was adopted into some other kazoku family.
Designations of both shizoku and heimin indicated family lines without any legal privilege, since the edict No. 29 of Dajokan (the Grand Council of State) of May 1872 had ordained that 'any family of sotsu class (another family rank used before Meiji Restoration) which had continued two or more generations were transferred to shizoku class and other sotsu families within one generation were reclassified to heimin.'
The designation of shizoku is associated with each family but not with an individual person, and, therefore, it is no wonder that not only any one who left a family of shizoku and entered other family but also any one who established a separate branch family had to lose the designation of shizoku of his former family and became heimin (Edict No.73 of 1874.)
Kazoku could receive special treatments from the state under public laws, but they were treated in the same manner as shizoku and heimin under private laws.
Although Edict No.44 of March 1875, had decreed that 'people may sign their names and titles with designations of their family's ranks, either kazoku, shizoku or heimin, in a prefecture,' an actual register of families had clear descriptions of kazoku and shizoku but no designation of heimin (Article 18 of the former Family Registration Law).
The United Kingdom
In the United Kingdom, people other than the King of England and peers are called commoners.
In this context, the term "peers" refers to the holders of peerage, and the followings are commoners:
Any one with only a courtesy designation is not a peer but a commoner. Any one without peerage, even if he is a member of a peer's family, is not a peer but a commoner.
Any one who holds a designation of either baronet, knight or other designation lower than baron is not a peer but a commoner, because neither of these designations are regarded as a peerage.
As in the case of William Mountbatten-Windsor, even a member of the British royal family without peerage is a commoner.
In the Republic of Rome, citizens other than patrici (patricians) were called plebs (plebeians). For reference, slaves were not considered citizens so that they were neither plebs nor, of course, patricians.