IDIOM WITH BETWEEN
Usually the preposition or the adverb "between" means "in or into the space separating two or more points, objects, people, ..... But the idiom with "between" is completely different: "between a rock and a hard place" = to be in a difficult position to make a decision
E.g: I don't want to tell my friend that I lost his book. He'll be angry if I tell him or angry if I don't. I am between a rock and a hard place.