What is Arrondissement?

Legal Definition
Arrondissement (/əˈrɒndɪsmənt/; French: [aʁɔ̃dismɑ̃]) is any of various administrative divisions of France, Belgium, Haiti, certain other Francophone countries, and the Netherlands.
-- Wikipedia
Legal Definition
In France, one of the subdivisions of a department
-- Black's Law Dictionary
Legal Definition
(French) A department subdivision.
-- Ballentine's Law Dictionary