What do you call the essential verb or phrase that cannot be left out of a sentence?

The essential verb or phrase that cannot be left out of a sentence is called the predicate.

Here's why:

* Predicate: The predicate is the part of a sentence that tells us what the subject is doing or being. It always includes a verb, and may also include objects, complements, and modifiers.

* Essential: The predicate is essential because it provides the core meaning of the sentence. Without it, the sentence wouldn't make sense or convey any information.

Example:

* "The cat sat on the mat."

* Subject: The cat

* Predicate: sat on the mat (The verb "sat" is the core of the predicate, telling us what the cat did.)

Let me know if you have any other questions!