MeaningWhen a married person had a special, secret relationship with someone who was not their husband or wife.
HistoryThis word comes from the Bible, where it is one of the Ten Commandments. It has always meant the same thing: for a married person to be with someone who is not their husband or wife.
Exampleבתורה כתוב "לא תנאף".
In the Torah it is written "You shall not cheat on your husband or wife."