Paywall
A paywall is a method of restricting access to content via a paid subscription. Beginning in the mid-2010s, newspapers started implementing paywalls on their websites as a way to increase revenue after years of decline in paid print readership and advertising revenue. In academics, research papers are often subject to a paywall and are available via academic libraries that subscribe.
Great Firewall
The Great Firewall is a form of trade protectionism that has allowed China to grow its own internet giants: Tencent, Alibaba, and Baidu. China has its own version of many foreign web properties, for example: Tencent Video (YouTube), Tencent Weibo (Twitter), Qzone (Facebook), WeChat (WhatsApp), Ctrip (Orbitz and others), Zhihu (Quora). With nearly one quarter of the global internet population (700 million users), the internet behind the GFW can be considered a "parallel universe" to the Internet that exists outside.