From China Digital Space

大中华局域网 (dà zhōng huá jú yù wǎng): The Great Chinese LAN (local area network)

The “Great Chinese LAN” sarcastically refers to the internet as it exists in China.

A local area network (LAN) is a computer network covering a small physical area, like a home, office, or small groups of buildings. The term ridicules how internet censorship has transformed the World Wide Web in China into nothing more than an isolated local area network.