What protocol is echo?

Could you please clarify what protocol is being referred to when we speak of 'echo'? Is it a specific communication standard used in computer networking, or is it perhaps a term related to the world of cryptocurrency and finance? I'm intrigued to learn more about its purpose, applications, and how it may factor into the broader landscape of digital transactions and interactions. Can you provide a concise explanation of the essence of 'echo' protocol and its relevance in our field?