Kosher food is food that follows the dietary laws of Judaism.
Raw fruits and vegetables are kosher.
There is only one restriction regarding raw fruits and vegetables: they must be rinsed well to make sure there are no insects or bugs on or inside the fruit or the vegetable. Insects and bugs are not kosher.
Fish
To be considered kosher, fish must have a fin and scales. Salmon and tuna are kosher. Dolphins are not kosher since they don't have scales. All kinds of seafood are not kosher.
There is no restriction in regards to the way the fish is being killed before it is cooked.
As long as the fish is cooked in a kosher environment - pots, pans, etc. - the fish is kosher and can be consumed.
Birds
Certain birds are kosher, most of them are not.
Kosher birds must have a redundant finger (sticking to the side), a crop and a gizzard that can be pealed. Roosters, hens, pigeons and ducks are all kosher. Eagles and hawks are not kosher.
Animals
Only a small group of animals is considered kosher.
A kosher animal is an animal that chews on its cud and has a split hoof.
Cows, goats and sheep are kosher. They chew on their cud and have a split hoof.
Horses are not kosher since their hoof is not split.
Camels are not kosher; they chew on their cud, they have a split foot but no hoof.
Pigs are not kosher; they do have a split hoof but they do not chew on their cud.
Lions and tigers have no hoof and they don't chew on their cud. Loins and tigers are not kosher.
In order to eat a kosher animal or bird, it must be slaughtered in a unique way, a technique that assures minimal suffering.
A Jewish professional slaughterer is called a Shochet. An ordained Shochet is a person who studied well the dietary laws of Judaism and the physiology of the animal. The knife the Shochet uses must be razor sharp, perfectly smooth, with no cracks or scratches at all.
Milk of a non-kosher animal is not kosher. The milk of kosher animals is kosher. Kosher dairy products must be produced from kosher milk; adding non kosher ingredients will make the final product non kosher.
Mixing dairy with meat is strictly forbidden.
Meat and dairy must not be cooked in the same pot and must not be eaten together in the same meal. After eating meat, one must wait a set period of time before consuming
dairy products.
Pots, pans, plates and utensils must be kosher as well. There must be a separate set of dishes for dairy and a separate set of dishes for meat. Dishes that were used to cook/serve non-kosher food considered non-kosher and should not be used in a kosher environment.
Foods that have no meat ingredients in them and no dairy ingredients in them are considered Parve and can be consumed with either dairy foods or meat foods.
Factories employ an ordained Kosher Supervisor - a person who is familiar with all the laws and the restrictions - that monitors the production process in the factory in order to make sure the final product is kosher.