The indentation is a 3mm space (more or less) that is left on all sides of the design to achieve a higher quality finish. This means that the graphics should always extend 3mm per side in respect of the finished product format. In the case of a 100 x 150mm card, for example, the cutting margin must measure 103 x 153mm.
The safety limit it is an imaginary margin of 5mm that goes between the cutting line and the beginning of the text or images in the design. This is done to avoid the cutting away of integral text or images.