gold: the precious yellow metal, whether as raw treasure, worked objects, or an idol's material
This is simply the ordinary word for gold, the precious metal, used in the parts of Daniel and Ezra that were written in Aramaic. It is the close cousin of the common Hebrew word for gold (זהב) and carries the same plain meaning.
Every time it appears, it points to the same thing: the physical metal. It is the gold of the temple vessels carried off to Babylon and later sent back, the "head of gold" on the towering statue in Nebuchadnezzar's dream, the giant golden image set up on the plain of Dura, the gold cups the king drank from at Belshazzar's feast, and the "gods of gold" his court praised. The settings differ, but the word does not: treasure, statue, drinking vessels, and idols are all just gold.
Where the metal takes on a larger meaning, that meaning comes from the story, not from the word. When the statue's golden head is said to stand for Babylon's empire, it is the vision that assigns the symbolism; the word itself never means more than the metal.