Suppose you want to show that two characters have some animosity towards one another. In some scene you set up a meeting between the characters in the elevator and an exchange of lines occurs. This develops as some kind of important factor that sets up the story in "Act 1: The Beginning". The exchange itself plays a significant role in Act 1 as do other scenes similar to it.
Is there a name for this exchange of dialogue?
PS. You can imagine this another way. In stand up comedy, sometimes, the comedian may chose to act out some funny situation between two or more characters that he plays out himself, taking turns to impersonate each character. This play is usually short, and has to have a very defined "conclusion" or gag. Is there a name for this exchange once it has made its point?