Schmaltz

Schmaltz (also spelled schmalz or shmalz) is rendered (clarified) chicken or goose fat. It is an integral part of traditional Ashkenazi Jewish cuisine, where it has been used for centuries in a wide array of dishes, such as chicken soup, latkes, matzah brei, chopped liver, matzah balls, fried chicken, and many others, either as a cooking fat, spread, or flavor enhancer.
Etymology.
Schmaltz is a noun derived from the German verb "schmelzen", meaning "to melt". The verb can be traced back to the Germanic root "smeltan", which survives in the Modern English verb "to smelt". The term entered English usage through Yiddish-speaking Ashkenazi Jews who used "schmaltz" to refer to kosher poultry fat; the word "shmalts" is the Yiddish word for rendered chicken fat. The English term "schmaltz" is derived from Yiddish and is cognate with the German term "Schmalz", which refers to any rendered fat of animal origin, including lard (more fully "Schweineschmalz") and clarified butter ("Butterschmalz"). English use tends to follow Yiddish, which limits its meaning to rendered poultry fat.
History.
Historically, chicken has been the most popular meat in Ashkenazi Jewish cuisine due to restrictions on Jews who often were not allowed to own land in Europe and thereby, were not able to tend to livestock. Schmaltz originated in the Jewish communities of north, west, and central Europe as it was an economical replacement for olive oil that typically was not available in these areas. Olive oil previously had an important role in Jewish culture. It had been used by the ancestors of the Ashkenazi Jews in their Ancient Israelite cuisine prior to the forced exile of Jews from Roman Israel, and it remained popular in Sephardic, and Mizrahi cuisines.
As olive oil and other vegetable oils (e.g. sesame oil, which Jews had used in Mesopotamia) were unavailable in northwestern Europe, Ashkenazi Jews turned to animal sources, like their Gentile neighbors. However, Kashrut prohibited Jews from using the most common cooking fats in northern Europe, namely butter and lard. Butter, being derived from milk, cannot be used with meat under the Jewish prohibition on mixing meat and dairy, while lard is derived from pork, a meat not considered kosher. Furthermore, even among the less common fats available, tallow derived from beef or mutton would have been uneconomical, particularly given that virtually all suet (the raw material for tallow) is "chelev" and its consumption is forbidden. Thus Ashkenazi Jews turned to poultry fat as their cooking fat of choice. This fat, which they called schmaltz, became the most popular cooking fat used in the shtetls (Jewish villages) of central and eastern Europe. It was commonly used in a multitude of dishes served with, or containing, meat in accordance with kosher dietary laws. The practice of overfeeding geese to produce more fat per bird produced modern Europe's first "foie gras" as well.
At the turn of the twentieth century, as the Ashkenazi Jews fled escalating antisemitism and persecution in Europe and sought refuge in the United States and other countries, they brought with them their traditional foods, including schmaltz. It remained popular in American Jewish cuisine until it fell out of common use over the course of the second half of the century due to the inconvenience involved in its preparation, health concerns regarding its saturated fat content, various diet trends, and aggressive marketing by Crisco of their vegetable shortening to the Jewish community of New York.
Over time, schmaltz was replaced with what often were vegetarian alternatives that were perceived to be healthier, such as the aforementioned vegetable shortening, then readily available olive oil, and margarine. Despite this, schmaltz remained in common use at Jewish delicatessens and Jewish restaurants as well as among those in the Haredi community.
Beginning in the twenty-first century, however, schmaltz regained much of its former popularity as various celebrity chefs such as Anthony Bourdain, Alon Shaya, Michael Solomonov, Joan Nathan, and others began to incorporate schmaltz into various dishes and recipes as part of emerging food trends popularizing long-forgotten Jewish foods. Schmaltz also began being used in various non-traditional ways, such as cornbread, chicken pot pie, and other foods as a flavor enhancer.
Process.
The manufacture of schmaltz involves cutting the fatty tissues of a bird (chicken or goose) into small pieces, melting the fat, and collecting the drippings. Schmaltz may be prepared by a dry process where the pieces are cooked under low heat and stirred, gradually yielding their fat. A wet process also exists whereby the fat is melted by direct steam injection. The rendered schmaltz is then filtered and clarified.
Homemade Jewish-style schmaltz is made by cutting chicken or goose fat into small pieces and melting in a pan over low-to-moderate heat, generally with onions. After the majority of the fat has been extracted, the melted fat is strained through a cheesecloth into a storage container. The remaining dark brown, crispy bits of skin and onion are known in Yiddish as "gribenes". 
Another simple method is as a by-product of the making of chicken soup. After the chicken is simmered in the pot or crock-pot, the broth is chilled so the fat rises to the top. Then the fat can be skimmed off, at once providing schmaltz to set aside for other uses and a lower-fat soup that is heated before serving.
Uses.
Schmaltz typically has a strong aroma, and therefore, often is used for hearty recipes such as stews or roasts. It is a key ingredient in Jewish soups such as chicken soup, as well as in matzo ball soup and some cholent. Sometimes it is used as a bread spread, where it may be salted. Generally, this is consumed on Jewish rye or challah breads. It may be used to prepare foods served as part of fleishig (meat) meals such as latkes, matzah brei, or potato kugel, or instead of butter when pan-frying potatoes, onions, or other foods.
Vegetarian schmaltz.
Various vegetarian (and consequently pareve) versions of schmaltz have been marketed, starting with Nyafat (U.S., Rokeach and Sons, 1924), which is largely coconut oil with some onion flavoring and color. Vegetable shortening also is used as a substitute.