腾云 is a literary term that literally means 'to ride clouds' — it describes immortals or deities in Chinese mythology and folklore traveling across the sky on clouds. In modern usage it appears mostly in xianxia fiction, historical fantasy, and poetic metaphors for speed or transcendence. You'll encounter it in phrases like 腾云驾雾 ('ride clouds and drive mist'), which describes flying through the air at supernatural speed.