Kaya (Skt. kāya; Tib. སྐུ་, ku, Wyl. sku) — the Sanskrit word kaya literally means ‘body’ but can also signify dimension, field or basis. This term designates the different manifestations or dimensions of a buddha.
The Tibetan word ku is the honorific term used to refer to an enlightened being's ‘body’, whereas lü designates an 'ordinary' person's body.