A bounding box is a 3D area where you want the mill to do its work or actually stay away.

This is useful for:

• Doing work in areas that require specific movements e.g. for more detailed finish ins small areas or higher speed of material removal for roughing in larger ones.
• Staying away from areas, f.i. to avoid clamps

You can set up to work inside the bounding box and outside the bounding box (plus another option editor has to look up, also not mentioned here where to find these settings in preferences).

The bounding box is shown in the model by a set of lines describing the box.