What does ERC-20 mean?

ERC-20, what does that mean? It sounds like some sort of technical jargon from the cryptocurrency world. Could you explain it to me in a way that's easy to understand? I've heard it mentioned in discussions about tokens and smart contracts, but I'm not quite sure what it stands for or what its significance is. Is it a standard or a protocol? And how does it fit into the broader ecosystem of blockchain technology and finance? I'm really curious to learn more about it.