Explanation:

A 'Terminal' is a hardware device that allows users to interact with a computer system, typically consisting of a 'V.D.U.' (Visual Display Unit, i.e., screen) for output and a 'Keyboard' for input. Option (d) 'Terminal' integrates these components to establish a user interface. Option (a) 'Printer' is an output device, (b) 'Mouse' is an input device, and (c) 'C.P.U.' is the central processing unit, none of which directly establish the link *between* a VDU and Keyboard as a combined interface. Thus, 'Terminal' is the correct concept.