Docker Holes are tiny pin holes punched into a commercial biscuit by a machine before baking.
The holes allow steam to escape during baking, thus helping to prevent the biscuit from inflating when you are aiming for a flat biscuit.
The technique is used in both savory items such as Saltine Crackers, and in sweet items such as Garibaldi biscuits.
Items with Docker Holes in them are often sold in perforated sheets from which you break off the ones you want.