"Oilseed" is a general term for plant seeds that contain a large amount of oil and are used as the raw material for vegetable oil. Main oilseeds throughout the world include soybeans, rapeseeds, sesame seeds, sunflower seeds, safflower seeds, cottonseeds, peanuts, and palm kernels.
Furthermore, although not technically seeds, rice bran and corn germ also contain oil and are used as raw materials for vegetable oil.

Olives and palms contain a large amount of oil in their pulp. They are used as the raw material for olive oil and palm oil respectively.

When focusing on the production region for oil-bearing raw materials, "tropical oil" is used as a general term for palm oil, palm kernel oil, coconut oil, and other oils which are produced in tropical regions and which are solid at normal temperatures. Also, the term "temperate oil" is used in Japan to refer to soybean oil, rapeseed oil and other vegetable oils.

"Raw oil" refers to the state of oil after compression or extraction from oil-bearing raw materials. However, "raw oil" as defined in international trade also includes oil which has been degummed. In general, raw oil is not appropriate for consumption.

Raw oil contains a variety of impurities that are undesirable for frying foods and for raw consumption. "Refining" is the act of removing these impurities. Refining includes processes such as degumming, deoxidation, de-coloring, and deodorization. Oil that has passed through these refining processes is called "refined oil. Also, in order to bring out the unique aroma and flavor of particular oils, some types of oil (virgin olive oil, roasted sesame oil, and akamizu (type of Japanese oil; translated as "red water") are not subjected to these refinement processes. Instead, these oils only undergo filtering or other processes to remove impurities.

"Salad oil" refers to vegetable oil which does not include constituents (natural wax, etc.) with a high melting point, is resistant to cold (do not solidify at any temperature), has a pleasant flavor, and has a light color. According to JAS (Japanese Agricultural Standards), salad oil remains clear for 5.5 hours at a temperature of 0 degrees Celsius. In addition to being consumed raw, salad oil is also used as an ingredient in mayonnaise, salad dressing, etc. Salad oil is manufactured by implementing a de-waxing process for vegetable oil that contains a large amount of constituents with a high melting point.

General term for oil made from a mixture of two or more types of oil.

From among refined oil, "tempura oil" is a general term for household oils. Currently, almost all vegetable oil intended for household use is salad oil. Therefore, the term "tempura oil" is now applied to certain types of vegetable oil for industrial use.
Recently, the term "tempura oil" is also displayed on oil that is based on salad oil, has a unique aroma, and is blended for a light flavor.

From among refined oil, "sirasimeyu" is a general term for industrial-use oils in the Japanese oil industry. Main examples include soybean sirasimeyu oil and rapeseed sirasimeyu oil. Literally translated as "white squeezed oil," this term originated from the white (nearly translucent) color of oil after rapeseed oil was heated (reheated) and supernatants were removed by oil wholesalers in Japan. The term was used in contrast to "red water" (akamizu), a type of oil that was widely available in Japan at that time.

Generally speaking, this term refers to rapeseed oil that has undergone mild refinement. Rapeseeds are roasted, expressed, washed in hot water, and then dried (moisture is removed) in order to produce an oil with the unique flavor of rapeseed. The name "red water" comes from the reddish color of the water. Mainly used for deep-frying tofu.

Refers to oil that is mechanically expressed from the pulp of oils without heating. This oil does not undergo any processing other than being washed in water, filtered, centrifuged, and decanted. From among virgin olive oil, "extra virgin olive oil" is a general term for oil that satisfies a certain standard of quality.

This olive oil is made by blending the virgin olive oil described above and refined olive oil This term is used only in Japan; overseas, it is simply called "olive oil."

"Processed oil" is a general term for edible vegetable oil that has undergone processing such as hydrogenation, transesterification, fractionation, emulsification, and plasticization. This creates characteristics appropriate for producing snack foods, baked goods, etc. According to JAS agricultural standards, the term "refined processed oil" is a standard defined for oils that have undergone hydrogenation, transesterification, and fractionation processing and satisfy a certain level of quality.

"Functional oil" refers to oil that has augmented with characteristics such as good thermal stability, low odor when heated, and other characteristics besides nutritional functions possessed by the oil itself.

Refers to oils with added aroma from spices, herbs, etc. Main examples include chili oil, garlic oil, onion oil, basil oil, and butter-flavored oil.

There is no clear legal definition for "healthy oil," it is a term coined on the commercial market.
Legally used terms are "Food for Specified Health Uses" and "Food with Health Claims." "Food for Specified Health Uses" is certified by the Minister of Health, Labor, and Welfare as possessing functions that maintain and promote health. "Food with Health Claims" (Ministerial certification not required) has been supplemented with nutrients which are often lacking from a normal diet.

"Meal" refers to the product obtained from oilseed lees from which oil has been extracted. Residue of solvents used to extract oil is removed from the lees, and the lees is dried and sieved to create meal. (In general, the name of the raw materials is added to the term meal, i.e. "soybean meal," etc.). Soybean meal is mainly used in blended animal feed, soybean protein products, and fermentation. Rapeseed meal is used in blended animal feed, organic fertilizer, etc.

Within the process for removing oil from oilseeds, it is possible to squeeze out a certain amount of oil by exerting strong pressure on rapeseeds and other seeds that possess a large amount of oil. This process is known as "compression." These lees contain a large amount of oil, and the process of eluting oil using solvents (n-hexane) is called "extraction." In the case of soybeans and other raw materials with a small amount of oil, only the extraction process is performed (compression is not performed). The term "pressure extraction" is used as a general term for both the compression and extraction processes. Also, the term "oil expression" is used to refer to both processes.

Refers to solvent used to extract oil in the extraction process discussed above. The oil manufacturing industry uses n-hexane, an organic solvent that is approved as a food additive.

Oil is mainly composed of three fatty acids which are bonded to glycerin (triglycerides). Transesterification is the method for changing oil properties by using oxygen or a chemical catalyst to perform inter-molecular or
intra-molecular replacement and realignment these bonded fatty acids. This makes it possible to manufacture processed oil that is appropriate for a variety of uses.

One method for improving the oxidation stability and changing the physical properties of oil. Hydrogen is blown into oil in the presence of catalysts and hydrogen is bonded to the unsaturated bonds of fatty acids. Depending on the degree of this hydrogen additive, it is possible to change the oil properties from liquid to solid. Main types of processed fats which utilize this function are margarine and fat spreads. Similar/related terms include "hardening" and "hardened oil."

Vegetable oil itself contains substances (tocopherol, tocotrienol) that prevent oxidation. Also, substances which possess antioxidant functions are added to further heighten oxidation stability. Tocopherol and BHA (butylated hydroxyanisole) are approved as an antioxidant by the Food Sanitation Act. However, according to agricultural standards of the JAS Act, these substances cannot be used as antioxidants in vegetable oil for household use.

One of the main constituents of oil, fatty acids are an organic acid consisting of carboxyl bonded to the end of a hydrocarbon chain (a bonded chain structure of carbon bonded to which hydrogen has bonded). The names of fatty acids (discussed later) are determined by the carbon number and unsaturated bonds in this chain. The majority of normal vegetable oils such as soybean oil and rapeseed oil have a carbon number ranging from 16 to 18, while tropical oils such as palm oil and coconut oil have a number from 6 to 12. The former is known as a "long chain," while the latter is called a "short chain."
Oils are the bond of glycerin and fatty acids (this bond is called a "glyceride"). In normal vegetable oil, approximately 96% to 96% of the total weight consists of triglycerides that are bonds of 1 glycerin and 3 fatty acids.

Fatty acids in which all carbons of hydrocarbon chains have saturated bonds are called "saturated fatty acids." This includes lauric acid, palmitic acid, and stearic acid. Conversely, fatty acids in which a portion of the hydrocarbon chain consists of unsaturated bonds (double bonds) are called "unsaturated fatty acids." Saturated fatty acids with a single double bond are called "monounsaturated fatty acids," while those with two or more double bonds are called "polyunsaturated fatty acids."
A main type of monounsaturated fatty acids is oleic acid, which is contained in large amounts in rapeseed oil and olive oil. Main types of polyunsaturated fatty acids are linoleic acid (divalent), which is contained in large amounts in soybean oil, etc., and α-linolenic acid (trivalent), which is contained in large amounts in linseed oil. The EPA and DHA which are contained in large amounts in fish oil are also types of polyunsaturated fatty acids.

"Essential fatty acids" refer to fatty acids that are required for physiological functions of the human body, but cannot be synthesized in the body and therefore must be externally obtained through food. From among polyunsaturated fatty acids, linoleic acid and α-linolenic acid are particularly important. Some people also view EPA and DHA as essential fatty acids because sufficient amounts cannot be synthesized in the human body.