In Ireland, these are typically in terraces and are exclusively considered flats / apartments. Invariably they are purpose-built and are not conversions. They are all ‘own door’ and do not share a common doorway like a typical apartment building. Most are 3-storey, but some are 4-storey. Sometimes they have individual gardens, but mostly they have shared grounds. Sometimes, the footprint of the ground floor unit is different from the upper unit.
I have always mapped the entire terrace as an apartment block. Some mappers may divide the terrace into “houses”, but tagged as apartments.
‘Terraces’ of 4-storey, 3-apartment ‘duplexes’ with 6-storey apartment blocks at the ends. Google Maps
Terrace of of 3-storey apartments. In this case, the end apartment is 3-storeys tall (L-shaped in elevation and likely 3-4 bedrooms), the next apartment is 1-storey tall (likely 1 bedroom).