Good question. In practice, they mean pretty much the same thing, but usage can vary depending on the region or context. Apartments in Spain https://worldestate.homes/en/spain/aparts/ usually refer to residential units in buildings, just like “flats.” Sometimes “apartamento” suggests a smaller, vacation-style unit, while “piso” is more commonly used for full-time living spaces. The key is checking the square meters, layout, and amenities. In newer buildings, you’ll get lifts, parking, and better insulation, while older blocks might lack those. I’d focus more on those practical features than the terminology itself.