A legal process server is someone who delivers the judicial paperwork or the service of process for a law firm, individual, corporation or organization based upon the rules of the court in the area in which the case is being held.
What is a subpoena?
A subpoena is an order of a court which requires a person to be present at a certain time and place or suffer a penalty (subpoena means, literally, "under penalty"). This is the traditional tool used by lawyers to ensure that witnesses present themselves at a given place, date and time to make themselves available to testify.