Short answers, pulled from the story.
Freedom of speech is a principle protecting individuals and communities from retaliation, censorship, or legal sanction for expressing their opinions and ideas. Article 19 of the Universal Declaration of Human Rights, adopted in 1948, defines freedom of expression as the right to hold opinions without interference and to seek, receive, and impart information and ideas through any media and regardless of frontiers.
England's Bill of Rights 1689 legally established the constitutional right of freedom of speech in Parliament, making it one of the earliest formal legal protections. Sweden passed a freedom of the press regulation on the 2nd of December 1766, which ended censorship and introduced public access to official records. The First Amendment to the United States Constitution enshrined freedom of speech in 1791.
Common limitations include libel, slander, obscenity, sedition, incitement, hate speech, classified information, and copyright violation, among others. Legal systems also apply time, place, and manner restrictions that balance speech rights against other rights or legitimate government interests. The harm principle and the offense principle are the two main philosophical frameworks used to justify restrictions.
John Milton published the influential Areopagitica in 1644, arguing against pre-censorship and for tolerance of a wide range of views. John Stuart Mill's On Liberty, published in 1859, became a landmark defense of free expression, arguing that truth drives out falsity and that suppressing speech is an injustice to a basic human right. Joel Feinberg introduced the "offense principle" in 1985 as a supplement to Mill's harm principle.
Brandenburg v. Ohio, decided by the U.S. Supreme Court in 1969, held that the constitution does not allow a state to prohibit advocacy of force except where such advocacy is directed to inciting imminent lawless action and is likely to cause it. The ruling expressly overruled Whitney v. California and discarded the earlier "clear and present danger" test, making protections for political speech in the United States close to absolute.
Internet censorship includes the control or suppression of information published or accessed online. China's "Great Firewall" operates through firewalls, proxy servers, and DNS poisoning and is directed by more than sixty laws and regulations. Reporters Without Borders identifies Mainland China, Cuba, Iran, North Korea, Saudi Arabia, and several other states as engaging in pervasive internet censorship.