Lascivious behavior

Lascivious behavior, better known as lewdness, indecency or lechery, is sexual behavior or conduct that is called crude and offensive. It is also against certain and other standards of appropriate behavior.
The legal usage.
Under American law, the word "lascivious" is a semi-technical term which means immoral sexual actions, words or thoughts. The term is often used under the legal description of criminal acts wherein certain forms of sexual activity are prohibited.
In the 2000s and after, the word was used for one of several adjectives describing pornography, solicitation for prostitution and indecent acts.
In American law mailing lascivious matter is prohibited thus:
Every obscene, lewd, lascivious, indecent, filthy or vile article, matter, thing, device, or substance ... [i]s declared to be nonmailable matter and shall not be conveyed in the mails or delivered from any post office or by any letter carrier.