flat roof
Refers to a roof that is horizontal or nearly horizontal, as opposed to a pitched roof. Common in architectural contexts.
This building has a flat roof, so you can go out onto the rooftop.
Compound of 陸 (roku, 'flat land') + 屋根 (yane, 'roof'). The exact historical derivation is uncertain, but the kanji combination directly conveys the meaning of a flat roof.