An essential oil is a concentrated hydrophobic liquid containing volatile aroma compounds from plants. Essential oils are also known as volatile oils, ethereal oils or aetherolea, or simply as the "oil of" the plant from which they were extracted, such as oil of clove. An oil is "essential" in the sense that it carries a distinctive scent, or essence, of the plant. Essential oils do not form a distinctive category for any medical, pharmacological, or culinary purpose.
Essential oils are generally extracted by distillation. Other processes include expression, or solvent extraction. They are used in perfumes, cosmetics, soaps and other products, for flavoring food and drink, and for adding scents to incense and household cleaning products.
The oils that are cold pressed and used on your salads are actual fatty oils that are the plant version of the fats found in in animal tissue.
Think of plant oil to be analogous to the fat that you get after cooking bacon or ground beef. The essential oils are like the musk oil that is produced by glands on some animals.
@additional - Ah. What you are seeing with the wheat germ oil is the same thing. They are both edible wheat germ oil.
The difference is that the one for cooking meets USDA standards as a food product. Meaning that all steps are in place to prevent contamination. to ensure quality, and to put it simply...make sure that it isn't going to cause food poisoning.
The wheat germ oil that is for cosmetic purposes has to fall under less strict guidelines as it will not be used for consumption.