"Thine" is an archaic English word that means "yours." It is often used in poetry and literature, particularly in works from the Middle Ages and the Renaissance. The term is a possessive form, similar to "your," and is typically used when addressing someone in a formal or affectionate manner. In modern English, "thine" is rarely used outside of historical or religious texts, such as the King James Bible. It reflects a time when the English language had different rules for pronouns, making it an interesting example of linguistic evolution.