"Mountain horn" is not a commonly used term in geology, biology, or any other field. It's possible you are referring to something else, or the term might be a local or informal name.

To help me understand what you're asking, could you please provide more context? For example:

* Where did you encounter this term? (In a book, a conversation, a movie, etc.)

* What was the context? (What were they talking about when they used this term?)

* Do you have any images or additional information?

With more context, I might be able to help you figure out what "mountain horn" refers to.