What is a sacred coffin?

The term "sacred coffin" is not a standard or widely recognized term in any specific religious or cultural context. It's possible you might be thinking of a different term, or it might be a term used within a specific, smaller group or tradition.

To help me understand what you're looking for, could you please clarify:

* What context are you interested in? Is it a religious context, a historical one, a literary one, or something else entirely?

* What are you trying to learn about the term? Are you looking for its meaning, its history, its significance, or something else?

Providing more information will help me give you a more accurate and helpful response.