MIL-STD-810, Environmental Engineering Considerations and Laboratory Tests, is a United States Military Standard that emphasizes tailoring an equipment's environmental design and test limits to the conditions that it will experience throughout its service life, and establishing chamber test methods that replicate the effects of environments on the equipment rather than imitating the environments themselves. Although prepared specifically for military applications, the standard is often used for commercial products as well.
The important point here is to understand that a MIL-SPEC certification does NOT mean that the device could resist battlefield conditions (meaning “in combat” or “on the frontlines”). That is why consumer devices look radically different from their military counterparts that are extra-bulky.
The MIL-STD-810G* drop test consists in testing the resistance to shock of all the equipment surface: all faces, edges, and corners. In total, 26 drops from about 4 feet (phones, laptops) are necessary to perform the complete drop test. Since tests are done to test specific areas of the equipment, manufacturers can divide the 26 drops over five different devices. After each drop, the equipment is inspected for damage.
Also, the drop surface is 2-inches of plywood (on top of concrete) because it is the most likely surface that things fall onto in a military transport context. In the real world, this may be different because people stand on concrete, metal or marble more so than on plywood. Not perfect, but good to know.
The “drop test” is also called “shock” tests in certain documents. These tests are designed to measure the durability of equipment during load/unloading and transportation.