A "throwaway line" refers to a casual or unimportant comment that is made without much thought or significance. It is a remark or statement that is easily overlooked or forgotten. Full definition
The fallout from the reveal is almost completely neglected and given a few throwaway lines in the beginning to explain what happened; the only person who has some great emotional payoff is Jughead. (theyoungfolks.com)
Here's the thing: every time a character is introduced, every time a seemingly throwaway line of dialogue is given that little extra emphasis, every time the classic three - act structure requires a very particular plot development... you know exactly what's coming next. (filmireland.net)
I hope to someday work with a larger press, and I'm completely open with Throwaway Lines about that plan. (emilysuess.com)