Based on the holly Quran, there are a few restrictions on what Muslim can not eat: pork, blood, any animal that is not slaughtered in the name of Allah and alcohol
So halal food is food that doesn’t violate the restrictions above.
Most non-Muslims know that Muslims can’t eat pork but very few people understand that halal is more than pork-free and alcohol-free. With the exception of seafood, any animal that is not slaughtered in the name of Allah is not halal. Chickens, cows, lambs, or turkeys can be non-halal when they are not slaughtered according to the Islamic guidelines. The Islamic guidelines require animals to be slaughtered by making incisions at the front of their throats using very sharp knives. The incisions should be deep and cut into the carotid artery, wind pipe and jugular veins to release all the blood from the body. The meat can only be consumed/processed after all the blood is drained from the body. When slaughtering an animal, the head of the animal has to be aligned to face the Qiblah and the butcher should utter a prayer “in the name of Allah”
With the growing demand of halal meat worldwide, more butchers are training to obtain halal certificates. Halal restaurants should obtain their meat supplies only from certified Halal butcheries.
Apart from getting the meat from Halal suppliers, food preparation is also important in determining whether or not a dish can be classified as halal. Any kitchen utensils like knives, spoons, baking tray or plates that have been previously used to prepare non-halal food should not be used unless they have been cleaned properly according to the Islamic guidelines.
Chefs should also refrain from using alcohol (wine, sherry, lager, etc) in their sauces. While people may argue that most of the alcohol will evaporate once the sauces are flambéed or simmered down, a lot of Muslims will not eat anything that has been “touched” by alcohol.
While it takes a great effort for restaurants to serve halal food, the demand is growing so rapidly that a lot of restaurants and food manufacturers do not mind doing the tedious process.