An editorial is an article that expresses the opinion of the person who or organization that wrote it. The president of the Llama Lovers Club wrote a scathing editorial in the Llama Times newspaper to protest the rash of llama thefts in her area.
Open up any newspaper, and you'll see page after page of articles. Most of these articles were written by journalists who assembled and reported the facts of the story. On the editorial page, however, you'll find nothing but opinion. That opinion might come from the editor of the paper, a local politician, or a concerned citizen who has found some important issue to discuss. Editorial can also refer to the editor of the paper, whose editorial decisions determine which articles — and editorials appear in each edition.