Vallis

Vallis is a Latin noun meaning valley. In planetary nomenclature, Vallis is used as a naming element to identify long, narrow depressions on the Moon and other solar-system bodies. The singular Vallis denotes an individual valley, while the plural Valles is used for broader valley systems or networks. Names are approved by the International Astronomical Union and follow classical Latin conventions.

On the Moon, examples include Vallis Alpes, a valley near the Mare Imbrium region; Vallis Schröteri (Schröter's Valley), a well-known sinuous rille; and Vallis Palitzsch, among others. On Mars, the prominent canyon system Valles Marineris represents one of the largest geological features in the solar system. The IAU uses the plural form Valles for such extensive systems on Mars, reflecting the Latin plural of vallis.

The use of Vallis as a toponym extends to other bodies, including Venus, where additional valleys are named under the same convention. The term is a standard part of planetary geology and nomenclature, serving as a generic linguistic label rather than a description of a single feature in itself.

In summary, Vallis functions as a formal naming element meaning valley in Latin, employed by the IAU to catalog and standardize long valleys and valley networks across the solar system, with notable examples on the Moon and Mars among others. Not to be confused, Valis (with a single L) is also a separate term referring to different, non-geological uses, such as titles in literature.