Wiktionary
n. (context sociology English) A social status that is the primary socially identifying characteristic of an individual, such as being the queen.
Wikipedia
In Sociology, master status is the social position that is the primary identifying characteristic of an individual. It is defined as "a status that has exceptional importance for social identity, often shaping a person's entire life"
The master status is often the most important in the architecture of individual identity. Common characteristics are those of race or ethnicity, sex, sexual orientation, physical ability, age, economic standing, religion or spirituality, and education. Others include raising children, employment status; and disability or mental illness.
In perception, an individual’s master status supersedes other identifying traits; for example, if a woman feels that her role as a mother is more important than her role as a woman, a daughter, etc., she is more likely to identify herself as a mother and to identify with other women who label themselves as such. An individual's master status dominates how they are perceived by others and their behaviour towards them. More than other aspects of the status set, the master status affects how the individual behaves and how others behave with respect to them.