Freedom of speech is a principle that supports the freedom of an individual or a community to articulate their opinions and ideas without fear of retaliation, censorship, or sanction. The term "freedom of expression" is sometimes used synonymously but includes any act of seeking, receiving, and imparting information or ideas, regardless of the medium used.
Freedom of expression is recognized as a human right under article 19 of the Universal Declaration of Human Rights (UDHR) and recognized in international human rights law in the International Covenant on Civil and Political Rights (ICCPR). Article 19 of the UDHR states that "everyone shall have the right to hold opinions without interference" and "everyone shall have the right to freedom of expression; this right shall include freedom to seek, receive and impart information and ideas of all kinds, regardless of frontiers, either orally, in writing or in print, in the form of art, or through any other media of his choice". The version of Article 19 in the ICCPR later amends this by stating that the exercise of these rights carries "special duties and responsibilities" and may "therefore be subject to certain restrictions" when necessary "[f]or respect of the rights or reputation of others" or "[f]or the protection of national security or of public order (order public), or of public health or morals".
Freedom of speech and expression, therefore, may not be recognized as being absolute, and common limitations to freedom of speech relate to libel, slander, obscenity, pornography, sedition, incitement, fighting words, classified information, copyright violation, trade secrets, food labeling, non-disclosure agreements, the right to privacy, the right to be forgotten, public security, and perjury. Justifications for such include the harm principle, proposed by John Stuart Mill in On Liberty, which suggests that: "the only purpose for which power can be rightfully exercised over any member of a civilized community, against his will, is to prevent harm to others."
The idea of the "offense principle" is also used in the justification of speech limitations, describing the restriction on forms of expression deemed offensive to society, considering factors such as extent, duration, motives of the speaker, and ease with which it could be avoided. With the evolution of the digital age, application of the freedom of speech becomes more controversial as new means of communication and restrictions arise, for example the Golden Shield Project, an initiative by Chinese government's Ministry of Public Security that filters potentially unfavorable data from foreign countries.