An absolute NC system is one in which all position coordinates are referred to one fixed origin called the zero point.

CNC machining, or Computer Numerical Control machining, is a subtractive manufacturing process that uses computer-controlled machine tools to create custom-designed parts. 

The basic steps of CNC machining are:
Create a 3D model of the design using CAD software
Convert the CAD file into a CNC program (G Code)
Set up the machine
The machine autonomously removes material from the workpiece to form the custom-designed part 
 

Related: Manufacturing Engineering Practice Test: NC Part Programming