"Maen nhw'n byw mewn tŷ teras hir."

Translation: They live in a long terraced house.

[y_ddraig_las]

Anyone know what a 'long terrace' is? I can only think of an 'end terrace' or 'link house'

[ibisc]

Perhaps Duo was just thinking of a house that is long, and in a terrace... bound to be one somewhere!

Or perhaps ... mewn tŷ mewn teras hir which would be quite common.

[y_ddraig_las]

okay so a long terrace is where you have lots of houses that are all roughly the same size in a long row, which is what most terraces are. Which is English should be 'a house in a long terrace' because the terrace is long, not the house.
It could also mean the shape, as most terrace houses I have lived in are narrow, but go back quite a way (are deep), then there is also confusion with longhouses. This is the fun of languages trying to translate between two completely different ways of describing a house.