An ecoregion is a relatively homogeneous geographic area "perceived by simultaneously analyzing a combination of causal and integrative factors including land surface form, soils, land uses, and potential natural vegetation.

(Omernik 1987, 123) Ecoregions "was coined by J.M. Crowley (1967) and popularized by R.G. Baily (1976) to define a mapped classification of ecosystem regions of the U.S....Ecoregions are generally considered to be the regions of relative homogeneity in ecological systems or in relationships between organisms and their environments".

Other /More definition:
An ecoregion is geographic areas that are distinguished from others by ecological characteristics such as climate, soils, geology, and vegetation.

Other /More definition:
An Ecoregion is Regions defined by similarity of climate, landform, soil, potential natural vegetation, hydrology, and other ecologically relevant variables.