Definition
Browser fingerprinting builds a persistent identifier for a visitor by combining dozens of small, individually unremarkable signals — operating system, browser version, screen resolution, installed fonts, time zone, language, GPU model, audio stack, canvas rendering quirks, and more. Each signal narrows the population of possible users; together they often produce a fingerprint unique enough to identify a single device with high confidence. The Electronic Frontier Foundation's research showed more than 80 percent of browsers tested had a fingerprint unique among the entire dataset.
Why a VPN Doesn't Stop It
A VPN changes your IP address but does nothing to alter the long list of attributes a tracker reads directly from your browser. From the website's perspective, you are the same browser making the request — you have just moved geographically. This is the single biggest blind spot in the popular belief that 'a VPN makes you anonymous.' A VPN protects the network layer; fingerprinting attacks the application layer.
Defending Against It
Mitigations include: using a browser that actively combats fingerprinting (Tor Browser, Brave, Mullvad Browser, hardened Firefox), disabling JavaScript on untrusted sites, blocking the canvas and WebGL APIs, and crucially — not customizing the browser too much, since unusual configurations make you stand out more, not less. The goal is to look like everyone else, which is why the Tor Browser is deliberately uniform across all its users.