An elusive concept used in the context of criminal law to describe a publication which is illegal because it is morally corruptive.
The common law has struggled with this word as society has evolved towards greater tolerance of alternative sexual behavior.
Historically, it included any lewd material which had no apparent social value, which was offensive to contemporary community standards of decency, and even material which tended to invoke impure sexual thoughts.
As an example of a modern definition, Canada has defined obscene material as any publication a dominant characteristic of which is the undue exploitation of sex, or of sex and crime, horror, cruelty or violence.
In Canadian criminal law, obsenec is defined at 159(8) of the Criminal Code:
"For the purposes of this Act, any publication a dominant characteristic of which is the undue exploitation of sex, or of sex and any one or more of the following subjects, namely, crime, horror, cruelty and violence, shall be deemed to be obscene."
In a 1987 case from British Columbia, Aldrich v. One Stop Video Ltd., 13 BCLR 2d 106, Justice Davies suggested, relying on several English dictionaries, and correctly, that what is captured by the term obscenity is a moving target:
"Obscenity comes from the Latin phrase ob caenum meaning about filth... It denotes the quality of the material identified as being offensive to modesty or decency....
"By definition, then, it is a reflection of moral values; but these values are subject to great change."