The word "whose" is a possessive pronoun used to indicate ownership or relationship. It helps to ask or clarify to whom something belongs. For example, in the sentence "Whose book is this?" the speaker is inquiring about the owner of the book. "Whose" can also be used in relative clauses to provide more information about a person or thing. For instance, in the sentence "The teacher whose students excelled received an award," "whose" connects the teacher to the students, showing a relationship of possession or association.