Ma'ruf (معروف) is a Qur'anic Arabic word meaning: that which is commonly -

• known
• understood
• recognized
• acknowledged
• accepted

The word is most often found in the Quranic exhortation "Amr bil Ma'ruf wa Nahy an al Munkar | امر بالمعروف و نهى عن المنكر." This is often translated as "Command the good and forbid the evil" but this translation fails to reflect the subtleties of the Arabic. Amr refers to the enforcement function of the duly constituted government of an ummah (community.) In this context, Ma'ruf, when applied to a particular law, means a law which is -

• known to the community (i.e. the community is aware of its existence)
• intelligible (understood by & makes sense) to the community
• generally recognized and commonly acknowledged as a good law
• accepted by the community as applicable to itself - the meaning of acceptance is strongly implied by the contrast with the word Munkar, which means "rejected."

There is a hadith in which Muhammad(P) is quoted as saying, "My ummah will never agree upon an error." This has been interpreted to mean that the consensus of the community is a source of moral and legal authority. See ijma.

Thus, a better translation of "Amr bil Ma'ruf wa Nahy an al Munkar" would be "Enforce that which is accepted [by the community], and prohibit that which is rejected."