A buckle that fastens to the watch strap and opens and fastens using hinged extenders. Invented by Louis Cartier in 1910. A deployant buckle is easier to put on and remove than a strap. Deployant comes from the verb "deployer" which means to unfold. Sometimes mistakenly referred to as a "deployment" clasp.
Deployment
1. the movement of troops or equipment to a place or position for military action. "the authorities announced deployment of extra security forces in towns and cities to prevent violence"
2. the action of bringing resources into effective action. "the rapid deployment of high-speed cable Internet services to consumers"