Islamic jurisprudence specifies which foods are halāl (حَلَال, "lawful") and which are harām (حَرَامْ, "unlawful"). This is derived from commandments found in the Quran, the holy book of Islam, as well as the Hadith and Sunnah, libraries cataloging things the Islamic prophet Muhammad is reported to have said and done. Extensions of these rulings are issued, as fatwas, by mujtahids, with varying degrees of strictness, but they are not always widely held to be authoritative.
According to the Quran, the only foods explicitly forbidden are meat from animals that die of themselves, blood, the animals that eat meat or feed on meat or skin like pig (pork), snakes etc. is unlawful.
Only cud chewing animals like cattle, deer, sheep, goats, and antelope are some examples of animals that are halal (lawful) and some lizards, only if they are slaughtered in the name of Allah.
However, a person would not be guilty of sin in a situation where the lack of any alternative creates an undesired necessity to consume that which is otherwise unlawful. (Quran 2:173) This is the "law of necessity", or in Islamic jurisprudence, "that which is necessary makes the forbidden permissible."
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