Is ERC20 Ethereum mainnet?

I'm quite interested in the intricacies of cryptocurrency, and I've come across ERC20 quite frequently. Could you clarify for me if ERC20 is indeed the mainnet of Ethereum? I've heard people mention it as such, but I'm still not quite sure. If it is, could you also explain what sets it apart from other blockchain networks? I'm eager to understand its significance within the Ethereum ecosystem and how it facilitates transactions and smart contracts. Thank you for your assistance in clarifying this matter for me.