What is the meaning of hisbah and rijaal al-hisbah?

We sometimes hear and read about hisbah (guarding against infringements) and rijaal al-hisbah (men who guard against infringements). Who are these men and what is their job?

Praise be to Allaah.
Rijaal al-hisbah (men who guard against infringements) are people who devote their time to denouncing visible evil whether they do that voluntarily or they are paid for it from the Bayt al-Maal (treasury) of the Muslims. Part of their job of hisbah is to denounce evil actions in marketplaces and elsewhere such as: 
1-      Free mixing of the sexes and wanton display of beauty (tabarruj) which are forbidden according to sharee’ah.
2-      Imitation of either of the sexes by the other.
3-      Men making approaches to women either verbally or by their actions.
4-      Profane, obscene or indecent speech.
5-      Playing radios, TVs or recorders etc. near mosques or in such a way as to disturb the worshippers.
6-      Non-Muslims openly manifesting their beliefs or the symbols of their religion, or showing disrespect towards the symbols and rulings of Islam.
7-      Displaying or selling pictures, books or video or audio recordings which go against Islamic etiquette or Islamic beliefs.
8-      Displaying 3-D or promiscuous images, or the symbols of non-Islamic religions such as the cross, the star of David, images of the Buddha, and the like.
9-      Manufacturing or promoting or trading in intoxicants.
10- Means that lead to immoral actions such as adultery, homosexuality and gambling, or running houses and places where evil and immoral actions may be committed.
11- Manifest bid’ah (innovation), such as venerating certain times and places for which there is no sanction in sharee’ah, or celebrating innovated, un-Islamic festivals and occasions.
12- Practising witchcraft, magic and trickery in order to consume people’s wealth unlawfully.
13- Cheating in weights and measures. 
Their work also involves the following: 
1-     Inspection of slaughterhouses to ensure that slaughter of animals is done in the manner prescribed in sharee’ah
2-     Inspection of boutiques and tailor shops catering to women. 
The presence of the police does not mean that there is no need for these rijaal al-hisbah, because the police force that exists in some countries does not denounce all evil actions and put an end to them. Rather they seek to enforce laws which at best include both truth and falsehood, whilst the rijaal al-hisbah enjoin everything that Allaah and His Messenger (peace and blessings of Allaah be upon him) have enjoined and compel people to adhere to the obligatory duties, and they forbid everything that Allaah and His Messenger (peace and blessings of Allaah be upon him) have forbidden, and they intervene to prevent forbidden actions.