清洁 (qīngjié) is a formal adjective meaning 'clean' — it's used for environments, air, or surfaces in a general sense of cleanliness. It's more formal and written than 干净 (gānjìng), which is the everyday spoken word for 'clean, tidy'. Unlike 纯洁 (chúnjié, pure in quality/morality) or 廉洁 (liánjié, honest in government), 清洁 focuses on physical cleanliness.