Definition
Metadata is information about a communication: the who, when, where, how long, and how much, as opposed to the actual content. Phone-call metadata is who called whom for how long; email metadata is sender, recipient, time, and subject; web-browsing metadata is which domains you visited and when. Modern intelligence and advertising practice has demonstrated that metadata is often as revealing as the content itself — sometimes more so, because it is highly structured and trivially queryable at scale.
What VPNs Hide and Don't
A VPN hides browsing metadata from your ISP and local network: they see only encrypted traffic to a single VPN server, not which sites you visit. The VPN provider, however, sees that metadata directly — they replace the ISP as the party with visibility. The destination website still sees per-session metadata: IP (the VPN's), user agent, time of day, frequency of return visits. End-to-end encrypted apps protect content but typically leak their own metadata (whom you message, when, how often).
The Core Trade-Off
Choosing a VPN is, in metadata terms, choosing whom you trust with your browsing patterns. A no-logs VPN in a privacy-friendly jurisdiction is a deliberate trust shift away from your ISP — usually a substantial improvement, but never a reduction to zero parties with visibility. For threat models that require eliminating metadata exposure entirely, Tor and similar onion-routing systems are the appropriate tool, with their own performance and reliability trade-offs.