There is a definite distinction between plagiarism (the unacknowledged use of someone else’s words claimed as one’s own) and fanfiction (the acknowledged or obvious borrowing of story elements to tell a new story in the fanfiction writer’s words.
By “obvious” we mean that even if a fanwork creator doesn’t include a disclaimer on their work, readers know that they did not invent Wonder Woman or Voldemort, or the phrase “Use the Force, Luke.”
Plagiarism is deceitful and prevents the original author from receiving credit for their own original work. Fanfiction and quotation are important fair uses which acknowledge the original author and their work. The OTW does not support plagiarism; we do support fanfiction and quotation.
To learn about how plagiarism is handled on AO3, refer to our Terms of Service FAQ.