What is OTC and ETD?

Could you please clarify for me what exactly OTC and ETD represent in the realm of finance? OTC, I've heard, stands for Over-The-Counter, but what does it specifically mean in this context? And what about ETD? I've seen it mentioned but I'm not quite sure what it signifies. Could you break down these terms for me, explaining their definitions, their applications, and maybe even give some examples to help me better understand them? I'm really interested in learning more about these financial instruments and how they operate within the broader financial ecosystem. Thank you for your assistance!