http://y7yea4pmqqtznb33qiugvysyn2bob5v62e4pvoadoibrwkq3tsddjeyd.onion/zh-hans/glossary/metadata
So the content of a message is not metadata, but who sent it, when, where from, and to whom, are all examples of metadata. Legal systems often protect content more than metadata: for instance, in the United States, law enforcement needs a warrant to listen to a person's telephone calls, but claims the right to obtain the list of who you have called far more easily.