What does Cielo means in spanish?

Cielo means sky or heaven depending on context.

Cielo is supposed to be spelled with a capital C when referring to heaven in the religious sense only. But it can get tricky. Sayings like "I'm in heaven" does not use the Word in the religious sense so "Estoy en el cielo" is spelled with the lower case c and technically translates back to English as "I'm in the sky."