1,980. What is Meant by Seclusion

Hilchos Sotah 1:2

The term seclusion in the Torah means entering into seclusion with the man about whom she was warned in front of witnesses not to do so. If they remain secluded together long enough to consummate relations, which is the length of time it would take to roast an egg and swallow it, then the woman is prohibited to her husband until she drinks the bitter water. Nowadays, since the test of the bitter water is unavailable, such a woman is prohibited to her husband forever; she is divorced without being paid the value of her kesubah.

Hilchos Sotah 1:3

If a man warns his wife against seclusion with two men at the same time, saying not to enter into seclusion with A and B, she is prohibited until she drinks the bitter water if she’s secluded with A and B at the same time for long enough to consummate relations. This is true even if A and B are her two brothers, or her father and her brother.