The background layer is the bottommost layer in the Layers palette. When you import an image from a scanner or digital camera, the entire image will be placed on the Background layer.
Background (in art and photography) The elements of an image might contain a foreground (A) and background (B). The background is the part of the image that is farthest from the viewer.
Background layer (in Photoshop) The bottommost layer in the Layers palette, the background layer is always locked (protected), meaning you cannot change its stacking order, blending mode, or opacity (unless you convert it into a regular layer).