The verse "You shall not commit adultery" from Deuteronomy 5:18 is a commandment prohibiting extramarital sexual relations. It's one of the Ten Commandments, a fundamental set of moral and ethical guidelines in Judaism and Christianity.

Here's a breakdown of its meaning:

Adultery: This typically refers to sexual intercourse between a married person and someone who is not their spouse.
Prohibition: The commandment is a direct and unambiguous prohibition. It's not a suggestion or a recommendation; it's a command that is not to be violated.
Moral and Covenantal Significance: The commandment highlights the importance of fidelity, commitment, and the sanctity of marriage. It underscores the idea that marriage is a sacred covenant between a man and a woman (in traditional interpretations).
Broader Implications: While the core meaning is about physical infidelity, some interpretations expand it to include emotional infidelity or any actions that betray the trust and commitment of the marriage bond.
Context: This commandment is part of a larger set of laws and principles designed to establish a just and moral society. The Ten Commandments are seen as a foundation for ethical behavior and a reflection of God's will.

In summary, "You shall not commit adultery" is a clear command against sexual relations outside of marriage, emphasizing the importance of fidelity and the sanctity of the marriage covenant.