Case

An ending or other modification attached to a noun or to a noun phrase to express its relation to the rest of the sentence. In English, case is exhibited only by a few pronouns: we say I saw her but She saw me, where I and me, and also she and her, are two different case forms of the same pronoun.

Nominative is the case-form used to mark a grammatical subject.

Objective is the case form used with certain pronouns to mark a non-subject.

Only the following pronouns distinguish a nominative form (the subject form) from an objective form: I (nominative)/me (objective); he/him; she/her; we/us; they/them; and who/whom. Other pronouns like you, it and what are invariable in form.