"An Editor-at-Large is a journalist who contributes content to a publication.

Unlike an editor who works on a publication from day-to-day and is hands on, an editor-at-large will contribute content on a regular or semi-regular basis and will have less of a say on a specific field such as layout, pictures or the publication’s direction.

However, unlike a writer, they are allowed their own preferences in the content they have to generate and don’t always have to pitch their ideas to the main editor. Though they are still subject to the direction and oversight of chief editors and executive editors, they frequently come up with ideas for other writers to research and write. "At large" means the editor has no specific assignments, but rather works on whatever interests them."
http://en.wikipedia.org/wiki/Editor-at-Large