heaven: the expanse above the earth, both the visible sky and the dwelling and rule of God
This is the Aramaic word for heaven, the close cousin of the common Hebrew word for the same thing. It appears only in the Aramaic parts of the Bible, in Ezra, Daniel, and one line of Jeremiah, and it always shows up in the same plural form that simply means the heavens.
Its range runs along one continuous line, from the sky you can see to the God you cannot. At the near end it is the open expanse overhead: the place where birds nest, where dew and wind and clouds come from, the height a great tree or a great empire is pictured reaching toward. At the far end it is where God lives and reigns, the place from which he sends his decrees and his messengers, and the source of the title used again and again in these books, the God of heaven.
The two are not separate words but two ends of one idea. Ancient readers looked up at the sky and understood it as the floor of God's own realm, so the same word names both. That is why a phrase like the birds of heaven and a phrase like the God of heaven sit comfortably side by side.
One step further, the word can stand in for God himself. When Daniel says that Heaven rules, he means that God rules, using the place as a respectful way to name the King without saying his name outright. This is the same habit of speech that later grows into the New Testament phrase the kingdom of heaven.