GFW is short for Great Firewall, national censorship of China’s Internet. Baidu removed all documents about GFW in its services, such as Zhidao (Answers), Baike (similar to wikipedia). When you try to search it, it returns no results at all. 

You may search “GFW” (within quotation marks) to get content.

But it’s hard to search anything throw Google China with GFW in keywords. The right way is typed ‘G F W’.

GSeeker says that Google’s technology is more advanced. XD

There are no proof shows that this accident was asked by government. Other search engines in China are normal to return results of GFW, such as Sogou, Yahoo China and IASK. (The top one in IASK is linked to Baidu Zhidao but disabled to open.)