noun
above-ground floor
Refers to any floor that is at or above ground level, in contrast to basement floors. Often used in building descriptions or real estate contexts.
このビルは地上階が5階まであります。
This building has five above-ground floors.
noun
ground floor; first floor
Specifically the floor at street level; equivalent to １階 in Japanese floor numbering. The cross-reference to １階 supports this meaning.
See also: １階
There is a café on the ground floor.
地下階 means 'basement floor' or 'underground floor', the direct opposite of 地上階.
Compound of 地上 (above ground) and 階 (floor). A straightforward modern term with no obscure historical derivation.