Run in the Background

What does "Running in the Background" mean in a Computer?

A program or application is "running in the background" when its algorithm is being executed by the CPU, but it isn't displaying a window on the screen, and doesn't appear in the taskbar.

In general, an operating system has several programs that run in the background at all times. Every time something happens while a window isn't being displayed is a program running in the background. For example, Windows will check for updates in the background, i.e. there is a program whose purpose is to check for updates, and it stays running in the background. If there is an update, Windows may display a window to tell you that there is an update available, but since this window isn't displayed while the "check for updates" algorithm was running, that part of the program was running in the background.

It's possible to minimize a window of an application so that it doesn't appear on the screen. We don't call this "running in the background," because the application will still appear on the taskbar. Amusingly, some applications will "minimize to the system tray" instead, becoming just a tiny icon on the bottom-right corner of the screen. In this case, some people do call this "running in the background," perhaps because it's not obvious that the task is running, or perhaps because some applications minimize to the system tray when you press the close button of their main window, so it feels like the application should have stopped running, but it "stays" running in the background.

Synonyms

A background process is another term for a program that always runs in the background.

A service is kind of a background process on Windows that can be easily configured to start running when the system starts. Services may be necessary for other programs to work properly, so they tend to stay running in the background all the time. Although services consume some memory, they typically don't consume a lot of CPU because they only do something when another program needs them to do something.

On Linux, the term daemon means the same thing as a service on Windows. By convention, names of daemon programs tend to end in d. For example, systemd, httpd, mysqld, dockerd.