Computer numerical control (CNC) is the system that drives a machine tool from a program: it says where to go, at what speed, with which tool and in what order. A machine fitted with it is a CNC machine tool (known in French as a MOCN).
The program is written in ISO code, known as G-code and M-code: G01 commands a straight-line move, M03 spindle rotation. The programmer writes it by hand for simple parts, but most often generates it with CAM software and a post-processor suited to the machine controller. Controllers such as Fanuc, Siemens or Heidenhain each have their own dialect and ergonomics. The machine moves its axes with servo motors and measuring scales, which gives a positioning accuracy counted in microns.
The major benefit is repeatability: apart from tool wear drift, the hundredth part is identical to the first. CNC also makes it possible to run 3D contours that are impossible by hand, to chain several operations together and to switch from one reference to another simply by changing program, which suits small runs. It is not limited to machining: it is also found on laser cutting machines, press brakes, punching machines and EDM. CNC machining workshops use it every day.
In a quote request. You do not have to supply a program: the drawing and the 3D model are enough (see the guide to file formats), and the workshop does the programming. If you want to get the program back or require a particular format, say so in the request, because it is not always provided for. For a repeat series, mention it: a validated program can be reused with every order.