CNC milling and CNC turning are the most commonly used machining styles in any given shop. Both rely on computer numerical control (CNC) programming, which directs the movement of a cutting machine along a predetermined path. Essentially, a CNC machine uses computer programming to cut away material in a specific way. The result is a part that is accurate and repeatable.
Milling and turning differ in very important ways, though. Milling removes material by advancing a tool that rotates incredibly fast into the stock material and the moving it along that CNC-determined path. Imagine a drill moving towards a piece of wood.
Turning, however, uses a lathe machine. On a lathe, the material is what spins while a stationary tool advances into it. Imagine a clay pot being made, spinning on a pottery wheel. The main difference between CNC milling and CNC turning is which piece spins: the cutting tool or the stock material.