The modern definition of Adultery sex with someone other than your spouse where you lie to and say you didn't have sex with them.
But if you do have sex with someone else and let your spouse know about it or what people call swinging ,it's not adultery.
When a woman cheats on a man that she is in a relationship with. Men nevercheat though, they only make new "friends"
I came home one day to find my wife with another man. She said it was payback for me cheating. I said i just made a new friend and she is the adulterer. So she committed adultery