Definition
Internet censorship is the deliberate restriction of internet content by governments, ISPs, or institutions. Methods range from outright blocking (China's blocking of Google, Russia's blocking of major news sites), to selective throttling, to keyword-based filtering, to legal pressure on platforms to remove content, to rate-limiting at choke points. The level of censorship varies enormously: open countries impose only narrow restrictions (court-ordered piracy site blocks, age verification); the most restricted (North Korea, Turkmenistan) maintain near-total information controls.
How VPNs Defeat Censorship
A VPN tunnel makes the original destination invisible to the censor. Instead of seeing 'this user is connecting to forbidden-news-site.com,' the censor sees 'this user is connecting to some IP in Switzerland.' The Swiss endpoint then forwards to the actual destination. As long as the censor cannot identify the VPN traffic itself or block the VPN endpoint, the bypass works. Where censors fight back with DPI and VPN-blocking, obfuscation and stealth modes restore connectivity.
The Limits
VPNs are an effective but imperfect tool. In the most aggressive censorship regimes, the cat-and-mouse game between censors and VPN providers means even the best providers experience intermittent outages. Local laws may make VPN use itself illegal or risky for users (China, Russia, UAE, Iran have varying degrees of legal restriction). For users in these contexts, the choice of provider, protocol, and obfuscation matters greatly, and threat-modelling is essential.