How much is 1 gwei?

Excuse me, I'm a bit confused about the value of cryptocurrency denominations. Could you clarify for me, how much exactly is 1 gwei in terms of the Ethereum blockchain? I've heard it's a very small fraction of Ether, but I'm not entirely sure about the specific value. It would be great if you could provide me with a straightforward answer to help me better understand this aspect of cryptocurrency transactions.