A distinct part of a larger organization, such as a government, university, or business, that is responsible for a specific area of activity. She works in the marketing department of the company.
A section of a store that sells a particular type of goods. I found the shoes I wanted in the sports department.
A particular area of knowledge or responsibility. Mathematics is not my department, but I can help you with history.
An administrative district or territorial division in some countries. They moved to the Dordogne department in south-western France.