Media blackout is the censorship of news related to a certain topic, particularly in mass media, for any reason. A media blackout may be voluntary, or may in some countries be enforced by the government or state. The latter case is controversial in peacetime, as some regard it as a human rights violation and repression of free speech. Press blackout is a similar phrase, but refers specifically to printed media.
Media blackouts are used, in particular, in times of declared war, to keep useful intelligence from the enemy. In some cases formal censorship is used, in others the news media may cooperate, as in the UK D- (later DA-)Notice system in the Second World War.