A group of words having a subject and a finite verb used as a part of a large sentence is a clause.
It is of three kinds.
1.Principle clause-which has a subj. And a finite verb and can express a sense alone.i.e.everybody hates him.
2.Subordinate clause-has a subj.and a verb and cannot express a sense without the principle clause.i.e. because he is a liar.
3.Co-ordinate clause-two ormore clause are joined with a conjunction.i.e.I went and met him.