The pattern of social classes in Hinduism.
Vedic scriptures speak of the idea that a person must be recognized as a caste to be a member. A worker could become qualified and become a priest.
However, the idea of Karma is such that a person may have become qualified to increase in caste because of past actions.
The basic castes are called "varn.as" or "colors":
Jâtis are subcastes (subdivisions) of the varn.as.