The People's Republic of China (does some things, or) uses different measures to control access to the internet. Some of these measures are specific laws, while other measures are technical. One of the technical measures is called the Great Firewall (GFW; simplified Chinese: 防火长城; traditional Chinese: 防火長城; pinyin: Fánghuǒ Chángchéng). China uses it to regulate the Internet domestically. Its role in internet censorship in China is to block access to selected foreign websites and to slow down cross-border internet traffic. The Great Firewall works by checking transmission control protocol (TCP) packets for keywords or sensitive words. If such words appear in the TCP packets, access will be closed. If one link is closed, more links from the same machine will be blocked by the Great Firewall. The effect includes: limiting access to foreign information sources, blocking popular foreign websites (e.g. Google Search, Facebook, Twitter, Wikipedia, and others) and mobile apps, and requiring foreign companies to adapt to domestic regulations.
Besides censorship, the Great Firewall has also influenced the development of China's internal internet economy by giving preference to domestic companies. The Great Firewall can also change the result of searches for problematic content. An example of this was when Ai Weiwei was arested. Sometimes the authorities ask big companies to remove content. One example of this was that they asked that Apple remove the publication Quartz from its Chinese app store. Quarts had reported on the 2019–2020 Hong Kong protests.
The term Great Firewall of China is a combination of the word firewall with the Great Wall of China. The phrase "Great Firewall of China" was first used in print by Australian sinologist Geremie Barmé in 1997.