Frequency: The word is one of the 1500 most common words in English.
Note: 'Whom' is used in formal or written English instead of ‘who’ when it is the object of a verb or preposition.
1.
You use ~ in questions when you ask about the name or identity of a person or group of people.
‘I want to send a telegram.’—‘Fine, to ~?’...
Whom did he expect to answer his phone?...
= who
QUEST
2.
You use ~ after certain words, especially verbs and adjectives, to introduce a clause where you talk about the name or identity of a person or a group of people.
He asked ~ I’d told about his having been away...
= who
CONJ
3.
You use ~ at the beginning of a relative clause when specifying the person or group of people you are talking about or when giving more information about them.
One writer in ~ I had taken an interest was Immanuel Velikovsky...
PRON: oft prep PRON