I have known, and used, the word 'twitten' since I was very small, it is a Surrey/Sussex word that is now occasionally found elsewhere on account of national mobility. However, I still find lots of people who have never heard the word.
A 'twitten' is simply a very narrow footpath; sometimes with houses on one side, but often without.
Here in Brighton they tend to be pathways in front of terraces of small (tiny) houses that have no road access. Perfect for those who haven't a car. This one above (Frederic Gardens) is a good example, as the houses have no tall walls in front, and can be photographed.
Another, with their backs opposite our house (Crown Gardens below), have the houses all hidden behind tall fencing, but peer over and you'll see that they're very 'cute'. Lady M rented one of these when she first attended the nearby Brighton Art College.
There are others that are equally beautiful, and they are highly sought after by commuters.
Oh to live in a Sussex twitten (with a tiny fire in a tiny hearth) now that Winter's here!
So, that's it. 'Twitten' explained.