In anthropological usage, ethnography is a genre of writing that
describes a cultural group based on in-depth observations, interviews
and participation. Ethnographies can be found in reference works,
edited volumes and journals, but the typical format is as an ethnographic monograph, which is a single book written by one person offering a holistic portrait of a single cultural group.
The word "ethnography" comes from the Greek ethnos = folk/people and graphein = writing.
NOTE: Ethnographies are a genre of writing created by anthropologists, but you may find that nowadays the term is used in a much looser way by other disciplines such as English or Education to mean something like "descriptive research." Many anthropologists, too, have moved far from the original meaning of the term. A study may be called "ethnographic" but still not qualify as an ethnography in the classic sense.
More information may be found on the web by typing "define:ethnography" into Google or by checking published reference works such as: