Halal is Arabic for permissible. Halal food is that which adheres to Islamic law, as defined in the Quran. It is frequently applied to permissible food and drinks. In Islam it means the things that are lawful to do according to the Islamic law. In Islam every single thing is listed under its law. The laws are halal and haram. Here halal means things that are allowed to do. Haram means forbidden. The daily chores we do like eatin,sleeping,talking etc.
But nowadays halal is a term commonly used for meat or food, because Muslims are not allowed meat that is not halal. The animals are categorized as halal and haram. The animals that eat the plant are halal like goat, sheep, beef etc. Most birds are also halal in addition to meat-eating birds such as eagle, vulture, crow etc. Carnivorous animals such as cats, dogs etc. are forbidden which means forbidden. Pork is forbidden in Islam. It is not a hygienic animal according to Islamic medicine. Even if the animal is not slaughtered, halal meat will be prohibited. For example mutton is halal but if the meat is of a goat who has died of disease then it is considered haraam like pork. So to eat the flesh of a halal animal, we should cut its throat and kill it. The explanation for this is that by cutting the throat the animal will die faster and most of the blood will be gone.