The word 'Halal' in ArabicA sign at a butcher's shop selling halal meat, in Paris.
Halal (Arabic: حلال, romanized:halāl, halaal, ħalāl) is an Arabic term meaning "permissible" Islam. The opposite is "haram", which means "forbidden".
Muslims have strict rules of what they may and may not eat:
Animals need to be killed in a special way. They must be slaughtered by a Muslim man, and the slaughter must be humane. (The animals should be slaughtered by hand so that all of their blood could be drained from them before they are eaten. The process is called "Zabihah Halal" in Arabic, meaning "Permissible Slaughter".)
Muslims may not consume carcass animals even the animal slaughtered by knife, not in its neck, called Mari' and wajadan. Hunting animals may be eaten but in a special manner.
They should not drink alcohol or consume other intoxicating substances in the wrong way (such as narcotics). Substances that change the mind, and that are not taken for medical reasons are forbidden.
Some sources even argue that caffeine, like alcohol and drugs, is forbidden.