A wallpaper or background is a digital image used as a decorative background on the screen of a computer.
On a computer it is usually for the desktop, while on a mobile phone it is usually the background for the ‘home’ or ‘idle’ screen.
Though most devices come with a default picture, users can usually change it to custom files of their choosing.
(The term desktop pattern was used to refer to a small pattern that was repeated to fill the screen.)
A mobile wallpaper is a computer wallpaper sized to fit a mobile device such as a mobile phone, personal digital assistant or digital audio player. The height is often greater than or equal to the width. Wallpapers can typically be downloaded at no cost from various websites for modern phones (such as those running Android, iOS, or Windows Phone operating systems). Modern smartphones allow users to use photos from the web; or photographs captured with a phone’s camera can be set as a wallpaper.
macOS has built-in support, via the Desktop & Screen Saver panel in its System Preferences, for cycling through a folder collection of images on a timed interval or when logging in or waking from sleep.
Additionally, macOS has the native ability to run a screen saver on the desktop; in this configuration, the screen saver appears beneath the desktop icons in place of the system wallpaper. However, macOS does not come with a built-in interface to do this; it must be done through Terminal commands or various third-party applications.
In Windows 7, 8, 8.1 and 10
Similarly, Windows can also be set to cycle through pictures from a folder at regular intervals. It is supported on Windows 7, Windows 8, Windows 8.1, and Windows 10.
Windows does not natively support animated backgrounds. However modern 3rd party software can be installed to have full support for GIF and AVI files. Wikipedia