Free speech is the right to express your ideas and opinions. In the U.S., publishing an opinion in a newspaper, wearing a black armband in protest, and contributing to a political campaign are all considered free speech.
Americans are guaranteed the right to free speech in the First Amendment to the Constitution. The idea is also considered a basic human right by the United Nations, although many people live in places where they aren't actually free to voice their opinions. Several countries punish citizens for writing or speaking against their governments. In the U.S., the right to free speech doesn't protect certain written or spoken words, including those that incite violence, promote fraud, or falsely damage a person's reputation.