Why is ETH not ERC20?

I've often heard the terms ETH and ERC20 mentioned in the same breath, but I'm still unclear on the distinction between them. Could you clarify for me? Is ETH not ERC20? If not, what are the fundamental differences between these two concepts? ETH, as I understand, is the native currency of the Ethereum blockchain, powering transactions and smart contracts. On the other hand, ERC20 seems to be a standard for tokens issued on the Ethereum network. But what does this mean in practical terms? Are ERC20 tokens a subset of ETH, or are they entirely separate entities? I'm interested in understanding the nuances of this distinction and how it affects the overall cryptocurrency ecosystem. Your explanation would be greatly appreciated.