noun
mean sea level
Technical term used in geography, oceanography, and surveying. Refers to the average height of the sea surface over a long period, used as a reference for elevation.
平均海水面は標高の基準として使われる。
Mean sea level is used as the reference for elevation.
この地図の等高線は平均海水面からの高さを示している。
The contour lines on this map indicate height above mean sea level.
Compound of 平均 (mean, average), 海水 (seawater), and 面 (surface). A straightforward technical term with no obscure historical derivation.