Plains have been defined as an extensive tract of flat land or a gentle undulating terrain without hills or depressions. Thus, plains may be said as lands with a maximum of gentle slopes and minimum of local relief.
In other words, plains are areas with local relief of less than 100 meters and slope angles of 5 degrees or less. Plains may also be defined as relatively low lands of the earth with comparatively small surface irregularities.
However, there is a lot of variation within the parameters defining plains. While some plains are nearly flat, others are rolling or undulating. There are also plains that are quite rough, though without steep slopes.
Plains are generally found at low elevations, though in some areas, particularly in mountainous areas they are found to rise well above 1500 meters.
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Plains are formed both by endogenetic forces as well as by the external processes of aggradations and degradation. There is wide variation in the size of plains. Some plains are of small size, while others are of great size.
Plains cover more than 50 per cent of the continental landmass, and they are found in all parts of the earth where there is land.
Besides, plains are situated in all climatic regions comprising hot and humid climate of the equatorial climate, and the dry and extremely cold climates of the Arctic borders.