What is a head phrase?

The term "head phrase" is not a standard grammatical term in English. It is likely a specific term used within a particular linguistic framework or theory.

To understand what "head phrase" means, you need more context. Please provide the following information:

* Where did you encounter the term? (e.g., a specific textbook, article, lecture)

* What was the context? (e.g., what were they discussing before introducing the term?)

* What is the larger linguistic theory or model being discussed?

With more information, I can provide a more accurate and helpful explanation of what "head phrase" might mean in that specific context.