{backgrounds} is used for questions concerning different ways and circumstances where color or images constitute a backdrop to other elements on a page.
Backgrounds are generally taken in the context of watermarks and other elements that the main content is typeset on the page.
backgrounds can also refer to the layering of different elements superimposed on top of each other. The bottom element is usually said to be on the background layer though it is just an ordering.
tikz is a popular package used to generate the background.
