We get our word pornography from this word. Nouns are translated harlot, whore, fornication, and whoremonger. It is used to describe all sexual relations outside of marriage. But this distinction is not really accurate. This forbids immorality on the part of the unmarried as well as married people.
Fornication is the broader term that includes all unlawful sexual intercourse.
Jesus replied by referring to their own laws and to Moses their leader and lawgiver. They well knew the teachings of the Law of Moses and the many grievances that had been taken to him. The Pharisees knew they, too, were guilty of similar treachery. They would have stoned her and let the man go free. Their own guilty conscience witnessed against them.