Your question is outside of the scope of this forum, but I'll answer it anyway.
In the context of the original question, "embed code" is a string of text that forms a command that allows a user to incorporate content of another Web page into his/her own Web page. For example, when you go to a Yahoo news web page that has a story, and in the middle of the copy, you have a video that actually resides in YouTube, but appears on this page, and you can play it. The embed code allows you to put an multimedia element into your page, so the reader does not have to navigate away and play the content.
Now, there is another sense of "embedded code", in the sense of "embedded systems". From Wikipedia: An embedded system is a computer system with a dedicated function within a larger mechanical or electrical system, often with real-time computing constraints. It is embedded as part of a complete device often including hardware and mechanical parts. Embedded systems control many devices in common use today. (
https://en.wikipedia.org/wiki/Embedded_system)
In the context of an embedded system, embedded code is the programming that controls an embedded system.
Finally, firmware is compiled software that is written directly into ROM, usually to run systems on a device. (See
http://techterms.com/definition/firmware)
From that standpoint, the embedded code of an embedded system could be firmware, but it is not necessarily so.
Saludos,
Enrique