Mil-Spec (short for Military Specification) refers to the military standard from the U.S. Department of Defense. When a product is compliant with these standards of sourcing, fabrication, material, quality and supply, it could be referred to as a Mil-Spec product or component.
The Luminox 3350 Series watch is built against the performance specification standard of MIL-PRF-46374G. This means that its water resistance, its robustness, and overall quality reflect the standards of the U.S. Department of Defense.