"Theirs" is a possessive pronoun in English. It is used to refer to something that belongs to or is associated with a group of people who have already been mentioned or are understood from the context. Here are some example sentences using "theirs": 1. The children played with their toys, and then they swapped some of theirs for each other's. (The children swapped some of their toys for toys belonging to other children.) 2. We each had a bag, but I left mine at home and borrowed one of theirs. (I borrowed one of the bags that belonged to the other people.) 3. The family enjoyed their vacation, and they said theirs was the best one they'd ever had. (The family referred to their vacation as "theirs" to indicate that it belonged to them.) In summary, "theirs" is a pronoun that refers to something owned or associated with a group of people, often used to avoid repeating the noun that the pronoun replaces.
