Device
A device is a machine, apparatus, or tool with comparatively simple specs. In the IT world, the term signifies either a battery powered machine with some particular function, or a computer's internal or peripheral apparatus.
In regards to the latter, computer-specific meaning, a "device" refers either to an internal apparatus configured with the CPU, memory, hard disc, video card, etc., or the keyboard, mouse, printer, monitor or other peripheral apparatus. A specific control software, known as a device driver, is required to run devices. The device drivers for the most common devices are generally included in the OS, but the device driver for new devices must often be installed onto the computer by the user.