Pareve is a Hebrew word which denotes a food product as containing neither meat nor milk ingredients. This is important in the practice of kosher, where milk and meat cannot be mixed during a meal. A food that is marked as Pareve is therefore free from a great deal of dietary worry, as it can be combined with most other things safely.
Modern Jewish law actually has an interesting definition of meat, in which fish are not considered to be meat. As a result, it can be said that fish are Pareve food, and therefore not subject to the same restrictions as fowl or other meats.
Eggs are something of a mixed area when it comes to their Pareve status. Eggs which come from kosher birds, which is to say, most non-carrion or non-carnivorous birds, are considered Pareve food. This is assuming they contain no blood, as blood is strictly prohibited under kosher law. Ashkenazi Jews also consider eggs which come from slaughtered birds to be of the same status as meat, and therefore not to be Pareve food.
Some additives in foods add an additional level of confusion when it comes to their Pareve food status. Calcium lactate, for example, may be derived either from milk or non-milk sources. In one case that might be considered Pareve food, while in another it would certainly not be.
Another problem comes from the FDA’s regulations with listing ingredients. If a small enough percentage of a product is made up of a certain ingredient, then that ingredient can be omitted from the ingredient list. This means that a product that might appear to be Pareve food, by having no meat or dairy listings, might actually contain small amounts of dairy or meat. Not enough to be required by law to list them, but certainly enough to make them non-Pareve by Rabbinical Law.
Yet another problem crops up because of shared equipment. Products may be produced on equipment that also processes dairy products, and therefore is not strictly Pareve food. These products may not list dairy in their ingredients, but trace amounts may make their way into the food. More producers are listing whether their foods are processed on shared equipment, however, making it easier to check for cross-contamination that might render a food non-Pareve.
Still, most Rabbis these days recommend erring on the side of caution when trying to decide whether a manufactured food is Pareve, and actually looking for the manufacturer’s Pareve marking, known as their hechshar.
Even a kosher and Pareve marking, however, can be questionable. There have been increasing complaints in recent years of manufacturers falsely presenting themselves as producing Pareve food when they are not. A number of foods, particularly from China, have been found to display the Pareve and kosher marks, but to actually contain dairy or meat ingredients. There are also growing complaints of certification bodies that are not particularly stringent in their testing, and so allow non-Pareve products to be labeled as Pareve food.
Ultimately, it is best to check for a hechshar from a reliable and consistent certification body when looking for a Pareve food. It is also recommended to make sure the producer is from a country where fraud is relatively low, such as most European nations, Israel, and the United States.