The unit of currency in Morocco is the Moroccan Dirham ; the Dirham is used in several Arab states, hence the contextual prefix. The Dirham, designated as MAD or Dhs, is comprised of 100 centimes; notes are available in denominations of 200, 100, 50, 25, 20 and (occasionally) 10 dirhams and coins are issued in denominations of 10, 5, 2 and 1 dirham, or 50, 20, 10 and 5 centimes. The word 'dirham' comes from the Greek 'drachma', one of the oldest currencies known to man, dating from the sixth century BC. The Greek drachma was circulated through trade in many countries around the Mediterranean, including Morocco, and in the 7th century the term 'dirham' was adopted widely throughout the Arab world.
The Dirham is officially designated a 'closed currency' which means that it can only be traded in Morocco, so if you have left over cash after your trip you'll need to convert it back before you leave or you may be stuck with useless money. According to Trip Advisor, however, Dirhams are traded in a number of travel agencies and airports outside of Morocco but only up to a maximum of 1000DH and one is likely to pay more for money exchange outside Morocco than within the country itself. It is wise to retain currency exchange receipts acquired in Morocco as they may be required when selling back surplus Dirhams at the airport prior to leaving (there is no limit to the number of Dirhams one can sell). If you'd prefer to exchange your money in Morocco, as most visitors do, you will be able to buy and sell currency at a Bureau de Change in the airport or port upon arrival in the country and also at banks.