"Thou" is an archaic second-person singular pronoun used in English, primarily during the Middle Ages and the Early Modern English period. It was commonly employed to address someone in a familiar or intimate manner, contrasting with "you," which was used for formal or plural contexts. In literature, "thou" appears frequently in works by authors like William Shakespeare and John Milton. Its usage has largely fallen out of everyday language, but it remains present in religious texts, such as the King James Bible, and in some poetic or theatrical contexts to evoke a sense of antiquity or formality.