A summons is a request or order for someone to show up, especially for legal matters. You could get a summons to testify at a trial.  A summon is a document issued by a court of law under its stamp and signature of the presiding judge of that court requiring the attendance of a person involved in a legal proceeding. When legal action is taken against a person i.e. a suit is filed against a person or a criminal complaint is lodged against him, such person is required to appear before the court on the date and time when the case is fixed for hearing.

Modes of summons:
1)Personal or Direct summon
2) Summon by the court 
3)Summon by plaintiff 
4) Substituted summon
5)summon by post