The definition of obscenity differs from culture to culture, between communities within a single culture, and also between individuals within those communities. Many cultures have produced laws to define what is considered to be obscene, and censorship is often used to try to suppress or control materials that are obscene under these definitions, usually including, but not limited to pornographic material. Because the concept of obscenity is often ill-defined, it can be used as a political tool to try to restrict freedom of expression. Thus, the definition of obscenity can be a civil liberties issue.
The United States has constitutional protection for freedom of speech, and the Supreme Court has ruled that this protection does not extend to obscenity as currently defined by the Miller test. In U.S. legal texts, the term "obscenity" now always refers to this "Miller-test-obscenity".
The etymology of obscenity and its parent adjective obscene, is not known, but is thought to have come from a primitive Latin word meaning "filth, foulness". Despite its long formal and informal use with a sexual connotation, the word still retains the meanings of "inspiring disgust" and even "inauspicious; ill-omened", as in such uses as "obscene profits", "the obscenity of war", and the like.
Many historically important works have been described as obscene, or prosecuted under obscenity laws. For example, the works of Charles-Pierre Baudelaire, Lenny Bruce, William S. Burroughs, James Joyce, D. H. Lawrence, Henry Miller, and the Marquis de Sade.