Answer:

• a unit of grammatical organization next below the sentence in rank and in traditional grammar said to consist of a subject and predicate.
• An independent clause - a clause that can stand alone as a sentence.
• A dependent clause - a clause that can't stand alone as a sentence, but supports an independent clause.
• Essential clauses modify key words and are important to the main point of a sentence. ... In English grammar, a clause is a part of a sentence that has its own subject and verb and that provides either essential or nonessential information. Thus, we have what are called "essential" and "nonessential" clause