The Background Render Element stores an image of the texture used in the background behind geometry in a scene as seen from the camera. Geometry that blocks the background image renders as black.
This render element interprets only a background texture, such as the texture set in the Environment Overrides, as a backgroundset as Env. Matte Texture (Render Settings > V-Ray > Overrides > Environment).
Other types of manually created backgrounds, such as a plane, mapped with a texture set outside a window, will not interpreted to be a "background" for the purposes of this render element.
