What is difference between a subpoena ad testificandum and a subpoena?

A subpoena is a legal document that orders an individual to appear in court or produce evidence. A subpoena ad testificandum specifically requires a person to testify as a witness in a legal proceeding. In contrast, a subpoena duces tecum compels the production of documents or evidence. Thus, the key difference lies in the purpose: one is for testimony, while the other can involve the submission of physical evidence.