According to the Merriam Webster Dictionary, an op-ed is "An essay in a newspaper or magazine that gives the opinion of the writer and that is written by someone who is not employed by the newspaper or magazine" and stands for opposite editorial. Op-Eds are sometimes referred to as Opinions and/or Commentary.
Image borrowed from Finger Lakes Community College
Purpose:
To discuss and provide arguments on issues of relevance to the readers of the newspaper, written by named authors not associated with the newspaper's editorial board.
How to Find:
In print newspapers, these articles are usually on the page opposite the editorial page (op-ed). In online databases, search for keywords related to the topic and look for document type limit: Commentary.