In narrative theory,
A third person omniscient narrator conveys information from multiple characters, places, and events of the story, including any given characters' thoughts, and a third person limited narrator conveys the knowledge and subjective experience of just one character.
I have been trying to find out who coined the term and in which publication but I have had no success so far. My first searches on Google Books and Google Scholar provided no answers, or at least none in publications that I can access online.
However, after discovering that Wayne C. Booth coined the term unreliable narrator in The Rhetoric of Fiction (1961), I found that Booth also mentions the term "omniscient narrator" in the same publication. Footnote 4 in the chapter "Telling as Showing" says,
"In novels we identify with the omniscient narrator" (Goodman, Structure of Literature [Chicago, 1954], p. 153. (…)
Unfortunately, a search using the terms "omniscient narrator" goodman "structure of literature" provides no results from Paul Goodman's book, which is out of print, so this turned out to be a dead end.
The novelist, he [Percy Lubbock, author of The Craft of Fiction] says, can either describe the characters from the outside, as an impartial or partial onlooker; or he can assume omniscience and describe them from within; (…).
Who is disposing the scattered facts, whose is this new point of view? It is the omniscient author, and the point of view is his—such would be the common answer, and it is the answer we get in Vanity Fair. By convention the author is allowed his universal knowledge of the story and the people in it.
Is this then the origin of the term or can older instances be found elsewhere?