Clause

            “A clause is a group of related words containing a subject and a predicate”
For example, he laughed.
A clause refers to a group of related words (within a sentence or itself as an independent sentence) which has both subject and predicate.

Example
            I will meet him in office.

The part of above sentence “I will meet him” is a clause because it has a subject(I) and a predicate(will meet him). On the other hand, the rest part of above sentence “in office” lacks both subject and predicate(verb) such group of word is called phrase.
A clause may stand as a simple sentence or may join another clause to make a sentence. Therefore, a sentence consists of one, two or more clauses.

Examples.

        • He is sleeping.                                                                (one clause)
        • The kids were laughing at the joker.                              (one clause)
        • The teacher asked a question, but no one answered.   (two clauses)
        • I am happy, because I won a prize.                               (two clauses)
        • I like Mathematics, but my brother likes Biology,
           because he wants to become a doctor.                         (three clauses)
Clauses are divided into main clause (also called independent clause) and subordinate clause (also called dependent clauses).