1. A program that is running without user input. A number of background processes can be running on a multitasking operating system, such as UNIX/Linux, while the user is interacting with the foreground process (for example, data entry). Some background processes daemons, for example never require user input. Others are merely in the background temporarily while the user is busy with the program presently running in the foreground. From I-gloss

2. A process that runs without interacting with a terminal. Because each user in a Linux system is allowed to have a number of background processes running simultaneously, Linux is called a multitasking system. From Linux Guide @FirstLinux