Outer London is the name for the group of London Boroughs that form a ring around Inner London.
These were areas that were not part of the County of London and became formally part of Greater London in 1965. An exception is North Woolwich, which was in the County of London but was transferred to Newham in 1965.
The position is now less clear, as the census and other statistical classifications use different definitions mainly because Newham and Haringey have many of the characteristics of Inner London boroughs while inner-London Greenwich is more like an Outer London borough.