Kashrut כשרות
The laws of permitted food: which animals, how they are slaughtered, and the separation of meat from milk.
The first dietary restriction precedes Sinai: the sons of Noach are forbidden flesh taken from a living animal. The full system is given in Vayikra and Devarim: animals with split hooves that chew the cud, fish with fins and scales, listed birds; blood and certain fats forbidden.
To this is added shechita — slaughter by a trained shochet with a flawlessly smooth blade — and inspection of the organs. A separate strand grows from the thrice-repeated «do not cook a kid in its mother's milk», from which the Oral Torah derives the ban on cooking, eating or profiting from mixtures of meat and milk, and hence separate utensils and waiting times.
The Torah gives almost no reason, saying only «be holy». The Rambam looked for medical sense in it; the Ramban insisted the point is the discipline of choice.