A reference to a source of information used in piece writing is called a?

A reference to a source of information used in piece writing is called a citation.

Here are some other terms you might encounter related to citations:

* Footnote: A citation placed at the bottom of the page.

* Endnote: A citation placed at the end of the document.

* Bibliography: A list of all sources used in a document, typically found at the end.

* Works cited: A list of sources that were directly cited in the text.

* Reference list: A list of sources used in a document, often formatted according to a specific style guide.

It's important to accurately cite your sources to avoid plagiarism and to give credit to the original authors.