An entity that is able to watch over all our actions in a unknown restrictive, controlling way with covert technology or other clandestine activities. It is commonly used to refer to a fear of the day when we will have zero privacy, due to government surveillance and personal accurate knowledge. The term was born from George Orwell's book "1984" where a government controls its citizens through continual surveillance.
The holy grail of any big brother type software is to measure or track the movements, associates and transactions of many people around the world, in as close to real time as possible. Such a system would be considerd too dangerous, because it would be suspectible to abuse.
Promis is an international surveillance database, which was used by multiple intelligence agencies during the mid 1980s and earlier. It contained backdoors so that Israel and the USA could spy on other countries including the spy agencies of Britain, Australia, South Korea, Iraq, and Canada.