Kosher foods are those foods that are approved to be taken as Jewish food according to the regulations of the Jewish Halakhic framework. In Judaism, these rules form the main aspect of the Jewish Dietary Law called Kashrut. The list of these foods and rules can be found in the Book of Leviticus.
Non-Kosher foods may be or may have been affected by any of the following:
• Foods that include the presence of ingredients from non-Kosher animals or from Kosher animals that were not properly slaughtered.
• Mixture of milk and meat
• Wine produced without supervision
• Produce from Israel that was not tithed
• Use of cooking utensils that had been used for non-Kosher food
Many of the laws of Kashrut in Judaism pertain to animals that can be eaten by the Jewish people. They teach, guide or direct which of the animals are clean (can be eaten) and filthy (should not be eaten).

Kosher food follows the laws of the Torah.

Kosher poultry includes chicken, goose, duck and turkey.

Kosher animals must have split hooves and chew their food. They must be killed in a ritual slaughter.

Kosher fish have fins and scales, and include tuna and salmon.

All types of rodents, reptiles and insects are unkosher.

Source: http://www.orthodox-jews.com/kosher-laws.html

Kosher food is any food that fits into the guidelines of consumption in accordance to the doctrines of Judaism. The basic laws regarding Kosher foods come from the book of Leviticus in the Bible in which distinctions between the "clean" and "unclean" foods are clarified. The food must be pure before consumption. The book of Leviticus not only describes the meats and seafood that should not be eaten, it also gives the guidelines for killing, preparing, and cooking the animals.

There has been some debate as to the relevance of kosher food in today's world and why it was included in the first place. It's understood that in Biblical times, the command to avoid particular foods protected the Israelites from certain diseases that were carried particular animals. Scavengers and birds of prey were strictly forbidden, as was slaughtering and ingesting an unconscious animal.

Others believe that the food stipulations were a way for the person to show his commitment to God by adhering to the Word of God. Others believe it was a lesson in self-control. Those involved in the Reformed Judaism sect are allowing that the foods are not banned, but adhering to the rules would be more spiritually rewarding. Another thought is that by restricting the food that could eaten, it helped distinguish the Israelites as being different from everyone else.

Kosher food is food that meets Jewish dietary laws or kashrut. This is the Hebrew word for "fit" or "proper" and any food can be called kosher if it adheres with the Jewish law or halacha.
But food that are typically labeled as "Jewish" are not necessary kosher.
Jewish foods are dishes are traditionally Jewish like Kreplach, cholent, kugle, latke, and kishka but if they are not prepared in accordance with kashrutit is not considered kosher food.

The work "kosher" is not only used for food. It basically means something that follows all the Jewish legal guidelines. This even gained a place in American slang that means appropriate, legitimate, or proper.

The laws of Kosher are rather extensive and some are directly derived from the bible and others have rabbinic interpretations.

These are some laws that governs kosher:
1. According to Torah, cloven hoofed, cud-chewing mammals are kosher. These are deer, sheep and goats while pig and rabbit ar not.
2. There are certain birds that are considered kosher in the U.S; these are chicken, duck, goose and turkey.
3. Fish and meat should not be served together
4. Milk and bet should not be served together
5. Processed foods must be prepared while there is a rabbi looking in.