Glossary of Mars features

The following definitions as used by Google Mars. This table serves as a starting point for more detailed descriptions of each Martian surface feature. Use examples from the Regions Category.

Term	Description
Albedo	Geographic area distinguished by amount of reflected light
Arcus, arcūs	Arc-shaped feature
Catena, catenae	Chain of craters
Cavus, cavi	Hollows, irregular steep-sided depressions usually in arrays or clusters
Chaos	Distinctive area of broken terrain
Chasma, chasmata	A deep, elongated, steep-sided depression (i.e. Candor Chasma)
Colles	Small hills or knobs
Crater, craters	A circular depression
Dorsum, dorsa	Ridge
Fluctus	Flow terrain
Fossa, fossae	Long, narrow, shallow depression
Labes	Landslide
Labyrinthus, labyrinthi	Complex of intersecting valleys
Lingula, lingulae	Extension of plateau having rounded lobate or tongue-like boundaries
Mensa, mensae	A flat-topped prominence with cliff-like edges
Mons, montes	Mountain (i.e. Olympus Mons)
Palus, paludes	small plain
Patera, paterae	An irregular crater, or a complex one with scalloped edges
Planitia, planitiae	Low plain (i.e. Chryse Planitia)
Planum, plana	Plateau or high plain
Rupes	Scarp
Scopulus, scopuli	Lobate or irregular scarp
Sulcus, sulci	Subparallel furrows and ridges
Terra, terrae	Extensive land mass (i.e. Terra Sirenum)
Tholus, tholi	Small domical mountain or hill
Undae	Dunes
Vallis, valles	Valley (i.e. Ares Vallis, Valles Marineris)
Vastitas, vastitates	Extensive plain

Original source: http://www.google.com/mars/glossary.html
Also from: http://planetarynames.wr.usgs.gov/jsp/append5.jsp