Pornography is broadly defined as written or visual material that stimulates sexual feelings whose primary purpose is to arouse the observer or reader. It is also referred to as porn, smut and obscene material.

The term "pornography" comes from porneia, the Greek word for prostitute, and means "the writings of and about prostitutes".

Defining the type of material that qualifies as pornography is more difficult. It is a relative term, subject to interpretation based on people's opinions. Standards of obscenity have been defined legally in a consistent way.

Technically, pornography is not illegal. Sexually explicit material that is judged in violation of the penal code is defined as obscene. These works are often called "hard core pornography", but even that is not illegal unless tested by the courts and found to be obscene.

The U.S. Supreme Court arrived at a definition of obscenity in the 1957 case of Roth vs. United States, and a number of lower courts have added their definitions since.

Pornography — Defining Erotic Material
Broadly speaking, erotic material is legally obscene if, for the average person:

• Its predominant appeal is to a prurient interest in sex
• It is contrary to the contemporary standards of the community
• It is without social value, or judged to be without artistic, literary, or scientific value

These standards may be helpful to an extent, but they are extremely difficult to apply in any objective way.

For one thing, standards vary from community to community and judgments about the artistic or literary value of material cannot be made by the use of a simple formula.

Whereas hard core pornography is understood to be strictly for commercial use, with no pretense to artistic merit, works of art are sometimes claimed to be obscene despite the defense of artistic value.