Final answer:
The period from October 1939 to April 1940 in France is referred to as the "drôle de guerre" or "phony war," a time of inaction characterized by anticipation of German aggression that didn't materialize until later.
Step-by-step explanation:
The Period of Inaction: Drôle de Guerre
The period during October 1939-April 1940 was known to the French as the "drôle de guerre," which translates to "phoney war" in English. In these months, the French military, bolstered by the Maginot Line defenses, awaited a German attack that didn't come until May 1940. This time was marked by little military action despite the state of war that existed between France and Germany after France had declared war following Germany's invasion of Poland.
While the French anticipated a German assault similar to World War I, the actual offensive by German forces when it commenced in May 1940 was characterized by rapid movement and the tactic known as "Blitzkrieg," taking the French and their allies by surprise. The inaction of the "drôle de guerre" thus gave way to a swift and disastrous defeat for France.