Censorship

According to Webster's Dictionary, to "censor" means "to examine in order to suppress or delete anything considered objectionable." The word "censor" originated in ancient Rome, where the government appointed officials to take the census and to supervise public morals. Censorship happens whenever some people succeed in imposing their political or moral values on others by suppressing words, images, or ideas that they find offensive.
A censor, traditionally, is an official whose job it is to examine literature, movies, or other forms of creative expression and to remove or ban anything she considers unsuitable. In this definition, censorship is something the government does. But censorship can also be accomplished very effectively by private groups.
Not all forms of censorship are illegal. When private individuals agitate to eliminate TV programs they dislike, or threaten to boycott the companies that support those programs with advertising dollars, they are certainly trying to censor artistic expression and interfere with the free speech of others. But their actions are perfectly legal; in fact, their protests are protected by the First Amendment right to freedom of speech.
Not even all government censorship is unlawful. For example, we still have laws against "obscenity" in art and entertainment. These laws allow the government to punish people for producing or disseminating material about sex, if a judge or jury thinks the material is sufficiently offensive and lacks any "serious value."