Is ETH ERC-20 compatible?

Could you please clarify if Ethereum, commonly referred to as ETH, is compatible with the ERC-20 standard? I've heard that ERC-20 is a technical standard used for smart contracts on the Ethereum blockchain that define certain rules and functionalities for tokens. However, I'm not entirely sure if all Ethereum tokens adhere to this standard or if there are exceptions. It would be helpful if you could explain the relationship between ETH and ERC-20, and whether ETH itself is considered an ERC-20 token. Thank you for your assistance in clarifying this matter.