From DT Online
Computer Numerical Control (CNC) describes the process by which Machine Tools are operated automatically by a computers linked to them. The computer output is interpreted as G-Code Commands and these instruct the Machine Tool which processes, with which tools and in what sequence it needs to operate to make the part.
Computers and Machine Tools linked in this way combine to become known as Computer Aided Manufacturing (CAM). Often the computer output is generated automatically from a Computer Aided Design (CAD) to create a CADCAM operation which in turn may be part of a wider Computer Aided Engineering (CAE) or Computer Integrated Manufacturing (CIM) enterprise and has led to the emergence of Concurrent Engineering practices.