Halal (or hallal) is an Arab word which defines what is allowed or licit for Moslems. Haram is the opposite of halal and thus defines what is prohibited or illicit to Moslems. These two terms cover all ordinary life fields and not only food.
However, apart from the Arabic and Moslem countries these two terms are strongly related to food. This is could be explained by the difficulty for Moslems living in these countries to find halal food and in particular halal meat.
Concerning food, certain products are intrinsically halal and others are intrinsically haram. The vegetables and the fruits belong to the first group, alcohol and pork or pig belongs to the second.
Meat can be licit only if the animal is licit (bovine, ovine, caprine, poultries, rabbits) and slaughtered according to Islamic law (zabiha). A food is halal only if all these components are halal. It is enough that a negligible quantity of a haram product is added to a dish so that it becomes itself haram.