FORNICATION: as voluntary sexual intercourse between persons not married to each other.

AND

ADULTERY: as voluntary sexual activity (as sexual intercourse) between a married man and someone other than his wife or between a married woman and someone other than her husband.

Listen to God's Word on the subject:

Now the works of the flesh are manifest, which are these; ADULTERY, FORNICATION, uncleanness, lasciviousness, idolatry, witchcraft, hatred, variance, emulations, wrath, strife, seditions, heresies, envyings, murders, drunkenness, revellings, and such like: of the which I tell you before, as I have also told you in time past, that they which do such things SHALL NOT INHERIT THE KINGDOM OF GOD. - Galatians 5:19-21(KJV)