The phrase refers to the government’s surveillance of the people with listening devices and cameras, in a totalitarian society, where Big Brother is the head of the totalitarian regime. Everyone in this society is under surveillance by the authorities, which reminds people of an endless catchphrase “Big Brother is watching You,” showing a dictator’s mindset of a Big Brother. Generally, the idea conveys a line of propaganda,  meaning citizens have to follow what a dictatorial government wants them to do, and if they do not, Big Brother will know, as it spies on them all the time.