A girl is born into a family that has traditionally been seen as middle class in her society. She takes a job as an entrepreneur and makes a great deal of money. She buys her family expensive cars and trips. Her family once shunned by a private club is now considered for membership. This demonstrates the phenomenon of social mobility.
Social mobility is the set of movements or displacements made by individuals, families or social groups within a given socioeconomic system. Sociology studies this phenomenon within the framework of the theories of social classes, social stratification, meritocracy and social status.
Ideally, societies should tend to have greater social mobility. This would mean that people who strive and have the merits (hence the association with the concept of meritocracy) can through this process improve their quality of life and climb the social ladder. In contrast, a society with low social mobility generates little hope of progress for its members, as people tend to retain the social status of their ancestors regardless of their personal effort.