天性 (tiān xìng) refers to the innate nature or natural disposition inherent in a living being, especially a person's inborn qualities. It is broader than 本能 (instinct), which is a specific biological drive, and more neutral than 本性 (true character), which often implies a moral or unchanging core. 性情 (temperament) focuses on emotional disposition, while 天性 covers the whole inborn makeup.