Groups and individuals are demographically described according to their statuses. There are two kinds of statuses: ascribed status and achieved status.
An ascribed status is totally outside of one's control: sex, age, race, birthplace, parental social status and whether someone is born as a slave or a free person are examples of ascribed status. Oftentimes one is born into an ascribed status. Achieved statuses, on the other hand, are based on decisions made by the individual and are generally voluntary: profession, education level and number of children are all examples of achieved statuses. The status set is all the statuses held by a person at a given time.
Ascribed statuses generally shape achieved statuses.
An African-descended, Mexican-born woman (three ascribed statuses) will unlikely ever become an Oscar winning actress living in New York City (three achieved statuses). However, Lupita Nyong'o achieved just that -- perhaps in some part due to another ascribed status of hers which serves as a privilege: being the daughter of a successful college professor.
Master status is the primary status by which society defines you.
In the United States, this is generally one's occupation. However, it could just as well be race or gender.