What if the first-second-third person system kept going?
In first person, the story is narrated by a character. “I head for the patch of wild mint. But I see them moving; something’s already in them.“
In second person, the story is narrated by an in-universe you. “You head for the patch of wild mint. Something is moving in them.“
In third person, the story is narrated by an unseen in-universe entity. “Kemi is headed for the patch of wild mint, but she notices something moving in them.“
In fourth person, the story is about someone reading the book. “Kemi goes for the patch of wild mint. But there’s something moving in them . . . what is it?“
In fifth person, the story is narrated by you reading the book. “You turn the page. You read that Kemi is moving towards the patch of wild mint, in spite of an unidentified entity.“
In sixth person, the story is narrated by an unseen entity watching you read the book. “Kathee turns the page. As she reads, she raises her eyebrows slightly.“
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Fun fact: There does exist a "fourth person".
Say you and me are talking about Felicia, when I want to introduce Cathy to the conversation. In English, both have the same grammatical person, and equally the same pronoun "she" (for those who mind, this is just an example). That means the only way I can refer to Cathy in topic of Felicia is by name, or other descriptive nouns (like "my friend").
However, some languages can distinguish Felicia and Cathy. In this case, Felicia is marked as a "proximate", which just means that she is the topic of our conversation. On the other hand, Cathy is marked as an "obviative", which just means that she is just a "side-character" on our conversation. The obviative is sometimes called a "fourth person" by linguists. (see Wikipedia)
Now, this is not the only definition of "fourth person". Another way people define fourth person is a third person that doesn't identify someone. In English, this is what the pronoun "the one" (or apparently "thon" by some lawyers) is used for.