A Lungo is like the opposite of a ristretto.
Instead of restricting the pour in a , a Lungo elongates and stretches the extraction to the point of . Anything longer would definitely be considered a Café Crema which is the same but an even longer brew again.
Where lungo ends and café crema begins is not entirely agreed upon. A normal espresso is considered primary extraction and thereafter is the secondary, less concentrated and less flavoursome extraction.
You can see the colour of the extraction get lighter, or ‘blond’, as the change between primary and secondary extraction occurs (after 30mls / 1 ounce from , 60 mls / 2 ounces from ).