In major newspapers, such as the New York Times[1] and the Boston Globe,[2] editorials are classified under the heading "opinion."
Other opinion pieces may be written by a (regular or guest) columnist.
An op-ed (abbreviated from "opposite the editorial page") is an opinion piece that appears on a page in the newspaper dedicated solely to them, often written by a subject-matter expert, a person with a unique perspective on an issue, or a regular columnist employed by the paper.
Op-eds may be solicited by the editorial staff, but may also be submitted by the author for publication.
Although the decision to publish such a piece rests with the editorial board, any opinions expressed are those of the author.