Data about data — who contacted whom, when, for how long, and from where
Metadata is data about data — information that describes the characteristics of a communication without including its content. For a phone call, metadata includes the numbers involved, the time and duration of the call, and the locations of the parties. For an email, metadata includes the sender, recipient, timestamp, subject line, and IP addresses. For internet activity, metadata includes websites visited, timestamps, device identifiers, and connection data.
Government officials have consistently downplayed the significance of metadata collection, arguing that it is less intrusive than collecting content. NSA Director Keith Alexander and other intelligence officials argued that metadata collection was not surveillance because the government was not listening to calls or reading emails. This framing was central to the legal justification for the NSA's bulk phone records program revealed by Snowden.
In reality, metadata is often more revealing than content. Stanford researchers demonstrated that phone metadata alone could identify individuals' medical conditions, political affiliations, religious practices, and personal relationships. Former NSA General Counsel Stewart Baker acknowledged: "Metadata absolutely tells you everything about somebody's life." Former CIA and NSA Director Michael Hayden went further: "We kill people based on metadata." The distinction between metadata and content, so central to the government's legal arguments, is functionally meaningless from an intelligence perspective.
