The Fae sometimes give gifts as rewards or as payment, often in the form of gold. They’ll also give gold if they’re trying to buy their way out of something. Unfortunately faeries can be known for their greed and their trickery, and they will sometimes disguise leaves or rocks or something else worthless as gold. The disguise is called glamour, a topic discussed in a previous post here. The ‘gold’ will eventually turn back into its old and useless form when actually used as gold.
On that note, there is a non-faerie related form of gold that miners call fools gold. Back when everybody was on the gold rush band wagon some miner found a large amount of what they thought was gold, but when they got it checked out it was just gold coloured rock. The rock was called fools gold as a result.