Probably any elevated narrow access way meant for occasional use might be called a catwalk, along the jib of a tower crane for example, but not an external access way to flats (apartments) – that would be a balcony to me too.
A walkway at ground level, needed to provide infrequently used access across wet or muddy ground, might be made from duck-boarding that looks like a picket fence laid on its side.
Breezeway is not a term you hear used much in the UK. I have heard it used by Australians to describe an opening left between buildings, or maybe only at ground floor level, to provide a fresh breeze to a back area. What the US calls a yard the UK calls a garden by the way, although we would use the term back yard to describe a flat concreted utility area – but there may well be regional differences in usage.
We use the term patio in the way ‘of troy’ described and to me it would probably be smaller than something I would call a terrace…but one man’s terrace is probably another’s patio!
Decks are becoming more popular here, but there used to be a catch-phrase from Henry Crun on the Goon Show: “You can’t get the wood you know.” This was a reference to the shortage of seasoned timber in the UK that has persisted since WW2. I am sure it is true to say that all decking is imported and therefore not cheap. Also, in our climate, patios, terraces and decking all suffer from algae growth (that slimy black mildew?) and it is a constant battle to keep them clean. I suspect cleaning may be more of a problem with decking than with concrete or stone.
