I'm listening to my car radio the other day, and this local DJ is talking about an upcoming interview with some sports figures. This is unusual for him, because he's a morning DJ and not the "sports guy"-- so he wants to do something entertaining for the regular listeners above and beyond the plain old interview. He starts explaining this "game"-- a show within a show, as it were, where he and his cohorts will use "code words" during the interview, but only regular listeners to the program will be in on the "joke." He even solicits people to call and suggest the code words that they would need to work casually into the conversation. As an example, he says "aluminum siding" and then gives a demonstration of how to work that into the conversation.
Sounds pretty inventive, doesn't it? Until you find out that whole bit, including that "aluminum siding" example, is practically taken verbatim from an old Steve Martin flick, Leap of Faith (1992).
When you take something from someone or someplace else and try to pass it off as your own, without acknowledging the original sources (homage) or adding some new twists or improvements to it (derivative work), then you are committing a rip off.