Is BNB ERC-20 or BEP20?

Could you please clarify for me if BNB is ERC-20 or BEP20? I've been hearing different opinions on this matter and I'm quite confused. I understand that ERC-20 is a standard for tokens built on the Ethereum blockchain, while BEP20 is a similar standard for tokens on the Binance Smart Chain. But what exactly is BNB classified as? Is it an ERC-20 token, a BEP20 token, or perhaps something else entirely? I'd really appreciate it if you could shed some light on this matter for me.