What is the meaning of al-Munkar and what are the conditions for denouncing it?

Everything that the Sharia deems ugly, forbids, and dislikes is a reprehensible act (munkar). The conditions for enjoining good and forbidding evil (al-amr bil ma'ruf wal nahy an al-munkar) are four pillars: the Muhtasib (the enforcer/commander), the person upon whom it is enforced, the matter upon which it is enforced, and the act of enforcement itself.

Conditions for the Muhtasib: He must be accountable (mukallaf), Muslim, and capable. This includes ordinary individuals, administrators, the immoral (fasiq), and women.

Conditions for the matter upon which it is enforced: Every reprehensible act that is currently present, manifest, and known to be reprehensible without requiring ijtihad (independent juristic reasoning).

Conditions for the person upon whom it is enforced: He must be a human being, and it is not a condition for him to be accountable (mukallaf) or discerning (mumayyiz).

Degrees of Enforcement (al-Ihtisab): [First is] recognizing [the munkar], then informing [the perpetrator], then forbidding, then admonition and advice, then verbal reprimand and harshness, then changing [the munkar] with the hand, then threatening with beating, then inflicting beating, then drawing a weapon, then seeking assistance from aides. The Muhtasib does not move to a higher degree except after exhausting the preceding one. Some degrees are exclusive to rulers, and denouncing is not permissible if it leads to a greater reprehensible act.