"The third-person omniscient point of view is a method of storytelling in which the narrator knows the thoughts and feelings of all of the characters in the story, as opposed to third-person limited, which adheres closely to one character's -- usually the main character's -- perspective." -study.com
omni - all, scient - knowing.
Basically,
In a third-person limited the narrator knows their own thoughts and feelings, but can only infer as to those of the rest of the characters.
In third person omniscient, the narrator knows the feelings and thoughts of, not only themselves but of all the characters present in the story.
