Green Borough is slang for the London Borough of Greenwich in South London.
It is nicknamed 'Green' borough because the council logo is green, the street bins are green, and 'Greenwich' contains the word 'Green'.
Neighbourhoods in Greenwich Borough are Thamesmead, Woolwich, Plumstead, Abbey Wood, Shooters Hill, Charlton, Greenwich, Kidbrooke, Eltham and part of Lee Green.
Green Borough is also sometimes used to refer to the London Borough of Bromley, also in South-East London. Neighbourhoods in this borough include Penge and Beckenham.
A: Where are you from?
B: I'm from Green Borough.