"An ethnography is a descriptive account of social life and culture in a particular social system based on detailed observations of what people actually do. It is a research method most closely associated with anthropological studies of tribal societies, but it also used by sociologists, especially in relation to groups, organizations and communities that are part of larger and more complex societies such as hospitals, ethnic neighborhoods, urban gangs, or religious cults."
-definition from the Blackwell Dictionary of Sociology.
Ethnographies are useful to give you a more detailed look on a group/organization you are researching. In this page, see a list of ethnographic books and journals that may be useful for your own research