What constitutes adultery for a Jewish married man?
Adultery, or Arayot in Hebrew, is the prohibited sexual relations a man or woman, married or not, can't have. The list appears in Torah, Vayikra 18 and 20. All those listed, will be punished with "Karet" and in addition, some carry the death penalty by Beth Din as well. The prohibition is not only on the intercourse but any physical contact of affection and even non-physical affection contact is a rabbinic prohibition. Among the list for men, are a married woman and a Niddah. (See Rambam Isurei Bia 1; Talmudic Encyclopedia, entry: Giluy Arayot)