A mama-san or mamasan is usually a woman in a position of authority, especially one in charge of a geisha house or bar or nightclub in Japan and East Asia.
The term is also used to refer to a woman who works in a supervisory role in certain establishments in Southeast Asia, typically those related to drinking places. Papa-san may be used to refer to a man in a similar position.
The term is a combination of the English word "Mama" and the Japanese suffix -san which is a polite honorific attached to a person's name or title, coined by U.S. soldiers in Japan after World War II. This probably has had some influence in its spread to other Southeast Asian countries.
The term mama-san in Japanese is not a polite reference to a mother and should never be used as such. Most Japanese children today call their mother mama, but the term does not persist into adulthood. The way to refer to one's mother, in Japanese, is okaa-san.
It is considered extremely rude to refer to a woman in charge of a respectable restaurant or inn as mama-san. The proper title for her is okami or okami-san.
To at least some extent, these can be considered the local equivalents of a madam, although the conventions of bar fine prostitution in Asia are quite different from those of street or brothel prostitution in western countries.
Mamasan (sometimes abbreviated MMS) is also used in the United States to refer to the woman managing the staff of Asian massage parlors.