Is Google carbon open source?

Excuse me, could you please clarify something for me? I came across the phrase "Google carbon open source" and I'm a bit confused. I understand that Google is a major tech company, and open source refers to software that's freely accessible and modifiable by anyone. But what exactly do you mean by "Google carbon open source"? Is it a specific project, a tool, or something else entirely? Could you elaborate on the context and purpose of this phrase? Thank you for your time.