Tube

But 'Tube' is used as shorthand for the whole network, not least by London Underground itself, … It tends to be older people who hold on to the distinction. A friend of mine was visiting his mother who lives about 500 yards from Parsons Green station on the District, which is a cut-and-cover line [not a tube line]. At the end of the evening she said, "How are you getting back?" He said, "Oh, on the Tube", and she looked at him absolutely blankly. "What Tube?" she said, "There is no Tube here."