Oxford English Dictionary
Viewpoint: A point of view: A mental position or attitude from which subjects or questions are considered.
Point of View: [after French point de vue] the position from which something is seen or viewed; (fig.) the perspective from which a subject or event is perceived, or a story, etc., narrated; . . .
Perspective: 5. The appearance of viewed objects with regard to relative position, distance from the viewer, etc. 9.a. The relation or proportion in which the parts of a subject are viewed by the mind; the aspect of a subject or matter, as perceived from a particular mental point of view. Now only: a particular attitude towards or way of regarding something; an individual point of view.
In fiction, viewpoint / point of view / perspective is the angle or vantage point from which a story is told.
first-person: The narrator is a character in the story and refers to himself as “I.”
second person: The reader is the main character. Narrator uses the pronoun “you” when referring to the main character.
third person: Neither the reader nor the narrator is the main character. Narrator uses the pronoun “he” or “she” when referring to the main character.
third-person omniscient: The narrator can tell what is going on in the minds of all the characters.
third-person limited: The narrator can tell what is going on in one or two of the characters, usually the main character.