What is any word phrase or clause that functions as a noun equivalent?

You're looking for a term that describes something that acts like a noun, even though it isn't a single word. There are several terms that fit this description:

* Noun Phrase: This is the most general term and encompasses any group of words that function as a noun. Examples: "the big red ball", "running a marathon", "that woman over there".

* Noun Clause: This is a clause (a group of words with a subject and verb) that acts as a noun. They often begin with words like "that", "what", "who", "where", "when", "why", or "how". Examples: "That he is happy" is good news. "What she said" surprised everyone.

* Gerund Phrase: This is a phrase that uses a gerund (a verb ending in "-ing" acting as a noun) as its head. Examples: "Playing the piano" is her favorite hobby. "Working late" is a common occurrence.

* Infinitive Phrase: This is a phrase that uses an infinitive (the base form of a verb preceded by "to") as its head. Examples: "To be happy" is her goal. "To run a marathon" is quite a challenge.

These are just a few examples. The specific term you use will depend on the specific structure and function of the phrase or clause within the sentence.