Adultery
The meaning—the ordinary meaning—of the word is making love to a woman you are not married to. But the real meaning of adultery is making love while you are not in love. She may be your own wife, but if you are not in love, then making love to her is adultery.
And man is a complex phenomenon: today you may be in love with your wife— yes, even with your wife! I know it is difficult, it is hard, and it is very rare too, but it happens. Today you may be in love with your own wife, and then making love to her is prayer, is worship, it is communion with God.
And this communion can happen even with some other woman to whom you are not married—if love is there, then it is not adultery. And if love is not there, then even what you are doing with your wife is adultery.
-Osho, "The Dhammapada - The Way of the Buddha, Vol 7, #3"