"predicative" is a word we use for nouns and adjectives that we put after copulas/linking verbs like "be" or "seem".
In "I throw the ball", "I" is the subject and "ball" is the object. I do the action, and the ball receives the action.
In "I am a teacher", "I" is the subject and "teacher" is the predicative. It doesn't receive the action of "being", it just redefines what I am.
Predicatives redefine the subject or object; they don't receive action.
Other sentences with predicatives:
She seems nice (nice).
They elected him senator (senator)
That made him angry (angry)