operating system (OS)
Computer software which handles the basic operation of a device, such as updating the display, communicating with hardware, managing files and running other programs.
Desktop and laptop computers typically come pre-installed with off-the-shelf operating systems such as Microsoft Windows, Mac OS, or Linux.
Tablets and smartphones are pre-installed with a mobile operating system such as Android or iPhone OS.
E-readers generally use custom-built operating systems that are unique to that particular reader or brand.