I didn't see the word plagiarism mentioned anywhere. That's overused, and means presenting someone else's work as your own, not ripping someone off by basing something on their work. If someone else had made the Gravity movie, then the studio took it and released it as theirs, that would be plagiarism, but not stealing plot ideas.
I guess I'm wandering away from the topic here (since the current issue seems more related to contract law than to the ethics of plagiarism)... but I'm not sure it's so cut-and-dried a definition. Plenty of people and academic authorities include the uncredited appropriation of ideas in their definition of plagiarism, not just the wholesale lifting of entire passages/works word-for-word.
"[I]t is considered plagiarism to draw any idea or any language from someone else without adequately crediting that source ... When you use your own language to describe someone else's idea, that idea still belongs to the author of the original material. Whenever you use ideas that you did not think up yourself, you need to give credit to the source in which you found them, whether you quote directly from that material or provide a responsible paraphrase."
Wikipedia and the dictionary on my Mac also make reference to the taking of ideas as plagiarism, so it doesn't seem uncommon to include ideas in the definition.
I didn't see the word plagiarism mentioned anywhere. That's overused, and means presenting someone else's work as your own, not ripping someone off by basing something on their work. If someone else had made the Gravity movie, then the studio took it and released it as theirs, that would be plagiarism, but not stealing plot ideas.