pronoun case
Whether a pronoun takes its subject form (I, who) or its object form (me, whom), based on the job it does.
Pronoun case is the form a pronoun takes depending on its grammatical role — the subject form (I, he, she, who) when it performs an action, or the object form (me, him, her, whom) when it receives one. "Who" is the subject form; "whom" is the object form.
Examples
The committee selected him, so whom (the object form) is correct: the candidate whom the committee selected.
See also