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) - In art or 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 Elements) - 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).