According to ArmyStudyGuide.com, there are five major terrain features: hill, ridge, valley, saddle and depression. Variations and combinations of these terrain types make up the topography of the Earth.
ArmyStudyGuide.com explains that a hilly terrain is characterized by small areas of high ground from which the earth slopes downward in every direction. A ridge is characterized by a single line of high ground with variations in height along its highest point. A ridge also is frequently mistaken for hilly terrain, but it is more than just a line of hills because the points of the crest are higher than the ground on all sides. A valley is characterized by level ground surrounded by higher ground. Valleys commonly feature streams and have a contoured U-shape.
According to Army Study Guide, saddle terrain is recognizable by a dip in the crest of a ridge, which may or may not be located between two hills. According to Discovery News, the desert terrain is another unique type of terrain with five subtypes: mountainous, rocky plateau, sand dunes, salt marshes and broken terrain. These variations are due to the extremely arid climate found in a desert terrain; these variations also affect the desert topography over time.