Running in the background is a mode of execution that is typical of some programs that do not require the presence or intervention of the user, and which may be concurrent to the execution of other programs (and therefore, it is only possible in multitasking systems), resulting in the user being unaware about it. Background programs typically perform long or time-consuming tasks such as peer-to-peer filesharing programs or defragmentation of filesystems. Many OS processes also run in the background.

In Windows, programs in this mode (scanning antiviruses or OS updates) often place an icon in the system tray (the area of the desktop next to the system clock) in order to signal their activity and adopt behaviors that reduce the use of resources so as to not interfere with the user's interactive activities, such as slowing down or causing interruptions. In Unix and Unix-like systems, processes that run in the background are called daemons. Using a task manager can highlight all running programs including those in the background.