This is the definition of discovery.

While a subpoena is a tool used in the discovery process to compel someone to produce documents or testify, it is not the process itself. The term "discovery" refers to the entire legal process by which opposing parties exchange information and gather evidence from each other before a trial. This process can include depositions, interrogatories, and indeed, subpoenas for documents. So, in the context of the question, "discovery" is the most accurate answer.

Discovery is the process, subpoena is a document.

3.1.3 Electronic Discovery pg. 48 - The Security Guidance for Critical Areas of Focus in Cloud Computing v4.0 U.S. rules around “discovery”—the process by which an opposing party obtains private documents for use in litigation—cover a wide range of potential documents.

3.1.3 Electronic Discovery pg. 48 - The Security Guidance for Critical Areas of Focus in Cloud Computing v4.0 U.S. rules around “discovery”—the process by which an opposing party obtains private documents for use in litigation—cover a wide range of potential documents.

Security Guide, page 49: On occasion, an actual cloud application or environment could itself be relevant to resolving a dispute. In these circumstances, the application and environment will likely be outside the control of the client and require that a subpoena or other discovery process be served on the provider directly.

Should a cloud service provider receive, from a third party, a request to provide information; this may be in the form of a subpoena, a warrant, or a court order in which access to the client data is demanded. Should be subpoena

C- Why is not Subpoena ? Un subpoena est l'injonction d'apparaître devant un tribunal pour produire un témoignage ou un document

Security Guide, 3.1.3 electronic discovery, page 48 ----> U.S. rules around “discovery”—the process by which an opposing party obtains private documents for use in litigation—cover a wide range of potential documents.