Final answer:
The collective noun in the provided sentence is 'droves.' It refers to many people acting as a unit to see movies. The use of singular or plural verbs with collective nouns depends on whether the group acts as one or individually.
Step-by-step explanation:
The collective noun in the sentence 'We turn out to see these movies in droves, and we've been doing the same thing as long as similar movies have been made.' is 'droves.' Collective nouns, such as audience, band, class, crowd, family, group, or team, refer to a group of individuals as a single unit and can take a singular or plural verb depending on the context. In this sentence, 'droves' is a collective noun that reflects a large number of people doing the same thing, i.e., going to see movies.