Wiktionary
think piece
n. An in-depth article that discusses a topic thoroughly and elaborates the writer's point of view, to inspire deep thought related to the article's subject. Think pieces are usually published in magazines, newspapers or web sites.
WordNet
think piece
n. an article in a newspaper or magazine or journal that represents opinions and ideas and discussion rather than bare facts
Usage examples of "think piece".
Here we bring you a new short one, a think piece that's slated to appear in her next book, Changing Planes.