Final answer:
The French referred to Vietnam, Laos, and Cambodia collectively as "Indochine."
Explanation:
During the colonial period, the French referred to the region encompassing Vietnam, Laos, and Cambodia collectively as "Indochine." This term, derived from the French words "Inde" (India) and "Chine" (China), reflected the French colonial control and administration over these territories in Southeast Asia. The term "Indochina" was commonly used to denote this geographical area during the period of French colonial rule.