Q. What does "uncited references" mean?
It means you are using information that doesn't appear to be your own knowledge and yet you are not telling the reader where you found that information.
You need to include a citation (either in-text -- at the end of the sentence or paragraph -- or in a footnote (if you are writing a History paper). And you need to include the full reference in your bibliography or works cited list at the end of your paper.