Editorial design is the way a page arranges words and images so people can follow a story or find information. It is used in magazines and books, and the same ideas can shape a website or article page.
A large heading can introduce the topic, a picture can set the scene, and smaller sections can guide the reader through the details. This is a bit like arranging a newspaper page so your eye knows where to begin.
Good editorial design is not only decoration. The order and emphasis should help readers understand the content, not distract them from it.