From AMS Glossary
The crescent-shaped upper surface of a column of liquid.
The curvature of this surface is dependent upon the cross-sectional area of the liquid and the relative ability of the liquid to wet the walls of the enclosure. For liquids that wet the walls of the enclosure, the curvature of the surface is concave. In the case of a mercury column enclosed in a glass container, the surface is convex, since mercury does not wet glass.