Pali is a Middle Indo-Aryan Prakrit language, closely related to but distinct from Sanskrit, that became the canonical language of Theravada Buddhism through the preservation of the Pali Canon, or Tipitaka, the earliest complete surviving Buddhist scriptural collection, whose composition and early transmission reflect the everyday spoken language of northern India in the centuries following the Buddha's life around the fifth century BCE rather than the more formal literary Sanskrit used by Brahmanical elites.
Pali's precise historical relationship to the actual dialect the Buddha himself spoke remains debated among scholars, since the language shows features associated with several different regions of ancient India rather than one clearly localized dialect, but Pali nonetheless became fixed as Theravada Buddhism's sacred canonical language once the tradition spread to Sri Lanka and mainland Southeast Asia, where the Pali Canon was eventually committed to writing around the first century BCE in Sri Lanka after centuries of oral transmission. Pali today functions purely as a liturgical and scholarly language, having no native speaker community, comparable in this respect to Latin's status within the Catholic Church.