It is refered to as a part of process of discovering facts before the trial beins. Usually a set of question in writing is presented to the witness by the law enforcers or by one party of lawsuit to the other party. Those question are answered by either the lawsuit party or witness under the oath in writing. Such answers are also considered evidence. Not all the parties are liable to answer the questions. But the ones directly connected to legal action are expected to reply in a specified period of time.