What holds a sword to the belt?

The term that describes the fastening mechanism used to attach a sword to the belt is known as a "frog." The frog is a specifically designed holder that allows the sword to be suspended from a belt or harness, providing both accessibility and security. In military contexts, especially within the USMC, the frog plays an important role in drawing the sword quickly while ensuring it remains securely attached.

Other components mentioned in the choices, such as a scabbard, are related to the sheath that encases the blade itself rather than how it is attached to the belt. A belt hook and a loop could refer to various fastening methods, but they do not specifically describe the traditional military attachment for swords, making the frog the most precise and appropriate term in this context.