A more thorough explanation:

Definition: Ad testificandum is a Latin term that means "to testify." It refers to a legal order that requires a person to appear in court and give testimony. This order is known as a subpoena ad testificandum. Example: If a witness is needed to provide evidence in a court case, they may be issued a subpoena ad testificandum. This legal order requires them to appear in court and testify under oath about what they know. The purpose of the subpoena ad testificandum is to ensure that all relevant information is presented in court and that justice is served.