Cite literature. You quoted an author's words or opinions, but you didn't find the original document. The words you quoted come from another author's article, which is a quotation.

Cited literature is a concept opposite to the original literature.

The original literature is the literature that the author must read in person. Only by consulting the original documents can we have a comprehensive, systematic and profound understanding of the original text, and it is also beneficial for readers to verify the context of the cited documents and decide the choice of documents.

Some paper authors refer to the references of related papers or books and copy them directly because of the limited number of periodicals in their units and the limited collection of books in the library, so they can't find the original documents. ?