Background typically refers to the rendering behind a container element's contents - usually on a web page, Windows form or other UI presentation medium.
In CSS, the background
property is a shorthand property for setting the individual background property values in a single place in the style sheet. This includes the image, color, tiling and position.
In Windows Presentation Foundation (WPF), the background attribute can be defined for any visual UI object. It should be noted that WPF applications use a background thread for handling rendering and repainting.
Desktop applications such as those written in .NET and Java may have colors or images used to fill the window of a particular frame or form.
For information about background threading, see the multithreading wiki.