Are USD and USDC the same?

Could you please clarify for me if USD and USDC are interchangeable terms? I've been hearing these two abbreviations frequently in discussions about cryptocurrency and finance, but I'm not entirely sure if they refer to the same thing. As a professional in this field, I'm sure you have a clear understanding of the distinction, if any. Could you elaborate on the differences between USD, the traditional US dollar, and USDC, which I believe is a stablecoin? It would be greatly appreciated if you could provide a brief description of each, highlighting any key differences between them. Thank you in advance for your assistance.