Criminal speech is a legal concept that identifies certain kinds of speech as a crime through promulgated laws or rules. Criminalization of speech is a direct pre-emptive restriction on freedom of speech (and the broader concept of freedom of expression).
In general, concepts such as criticism of government and criticism of royalty are sometimes controversially included under the umbrella of criminal speech. In contrast, prohibitions on shouting fire in a crowded theater (as a practical joke, not as a warning) are not generally considered controversial given the potential for imminent harm.
Laws vary by country in accordance with the legal principles that form the basis of their system of jurisprudence. Authoritarian governments most commonly use criminalization of speech to aid in suppression of dissent. In many democracies, the concept of hate speech has emerged in recent years, to counteract the political and social influence of hate groups.