1 The preferred linear route along which surface water and groundwater flow is usually concentrated (although water can flow across wide, flat surfaces as sheet flow). It is commonly a linear, concave-based depression (e.g. river channel, submarine fan channel). The geometry may be sinuous, anastomosing, or straight, and with a widely variable width-to-depth ratio. See braided stream; and meander.
2 A narrow sea-way connecting two wider bodies of water (e.g. the English Channel).
3 In remote sensing, the range of wavelengths recorded by a single detector to form an image.