What does subject pronoun means

They replace nouns that are subjects like i,you,he,or she

A pronoun is a word taking the place of a noun (I, it, they, s/he, all, etc)

A subject is the thing that is doing something in the sentence (ie in “George ran down the street” who ran down the street? George. George is the subject)

Therefore, a subject pronoun is a pronoun taking the place of the subject.

UNLESS, they are asking for the subjective personal pronouns. Which are I, she, he, it, we, and they.