This type of data is called metadata

README.md

@@ -5,7 +5,7 @@ Bitmessage is a P2P communications protocol used to send encrypted messages to
 another person or to many subscribers. It is decentralized and trustless,
 meaning that you need-not inherently trust any entities like root certificate
 authorities. It uses strong authentication, which means that the sender of a
-message cannot be spoofed, and it aims to hide "non-content" data, like the
+message cannot be spoofed, and it aims to hide metadata, like the
 sender and receiver of messages, from passive eavesdroppers like those running
 warrantless wiretapping programs.