"Whom" is a pronoun used to refer to the object of a verb or preposition in a sentence. It is often used in formal contexts and is less common in everyday speech. For example, in the sentence "To whom should I address the letter?", "whom" is the object of the preposition "to." In contrast to "who," which refers to the subject of a sentence, "whom" helps clarify who is receiving the action. Understanding when to use "whom" can enhance clarity in communication, especially in writing. It is often associated with more formal language, such as in legal documents or literature.