Where Do I Go From Here? - 3D Printing: Build your Own 3D Printer and Print your own 3D Objects - page 201

Most CNC machines work like 3D printers—a series of motors move the milling
bit around on the workspace. Unlike the Simple, however, where it's the print bed
that moves left and right (instead of the hot end moving left and right), most CNC
machines don't move the workspace. Instead, the milling bit moves in all three
directions. The milling bit shown in Figure 11.2 moves left and right, forward and
backward, and up and down; the workspace stays put.
Figure 11.2 Movement of the milling bit occurs in all three directions.
This is a 3-axis CNC machine. It moves along the X, Y, and Z axes. But there
are more advanced CNC machines called 4-axis that also allow for rotation like
a lathe. It's a bit beyond the purposes of this discussion; just be aware that CNC
machines have been around longer and are much more advanced, offering more
features and tools than 3D printers do.