According to the consensus of classical Islamic scholarship, the term **Zina (الزنا)** refers to any illicit sexual intercourse between a man and a woman who are not lawfully married to each other. It is unequivocally classified as a *Kabirah* (major sin) and is one of the most severe offenses in Islamic law and ethics. The Quran's definitive prohibition is found in Surah Al-Isra (17:32): **"And do not approach unlawful sexual intercourse. Indeed, it is ever an immorality and is evil as a way."** Ibn Kathir explains that the command "do not approach" is a more profound prohibition than simply "do not commit," as it forbids all the preceding actions and pathways that could lead to the act. Al-Qurtubi's analysis of the legal verses, such as 24:2 which prescribes one hundred lashes for the unmarried fornicator, highlights the social gravity of the crime. The wisdom behind this strict prohibition, as synthesized from the Quranic verses that encourage chaste marriage (e.g., 4:25, 5:5), is to preserve lineage, protect family honor, maintain social stability, and uphold the sanctity of the human being. It channels human desire towards the responsible, dignified, and blessed institution of marriage.