Final answer:
A restrictive element is essential to the meaning of a sentence and is not separated by commas.
Step-by-step explanation:
When a descriptive word, phrase, or clause is essential to the meaning of a sentence, it is considered restrictive. A restrictive element provides necessary information that cannot be removed without changing the meaning of the sentence. It is not separated from the rest of the sentence by commas.
Learn more about The nature of restrictive elements in sentences