All olive oil starts with fruit on a tree. What happens after the fruit and the tree part company makes all the difference to the oil produced.
United States Department of Agriculture the only acceptable grade of olive oil is Virgin Olive Oil per the US Department of Agriculture. The Food and Drug Administration definition is, “Olive oil is the edible oil expressed from the sound, mature fruit of the olive tree." No recognition is given to refined or extracted oil.
The two ways to assess virgin olive are chemical and organoleptic analysis. They are both equally important although one is totally objective and the other is totally subjective. Laboratory analysis informs us of the levels of beneficial polyphenols and oleic acid, and the products of deterioration free fatty acids and peroxide. But it cannot indicate anything about the pleasure of using fresh, well produced oil.
Organoleptic analysis happens in the nose and mouth of the taster, either professional or with you, our customer. Aesthetic notes of fruity, nutty, fresh grassy, peppery, and many, many others are there in varying balance that give complexity to the oil and appeal in different ways to each person. Laboratory analysis can track down the chemical nature of those flavors and aromas, but the human sensory system is still the best organoleptic analysis device. We recommend that you give yourself the opportunity to taste and assess many olive oils in order to educate your palate and help you find the oil that gives you the most satisfaction.
Most grading is based on the method of production and designations are a marketing tool used by producers. The terms can be confusing and sometimes intentionally misleading. Once again it is important to know as much as possible about what you choose.
Extra-virgin olive oil comes from virgin oil production only, contains no more than 0.8% acidity, and is judged to have a superior taste. Extra Virgin olive oil accounts for less than 10% of oil in many producing countries.
Virgin olive oil is produced by the use of physical means and no chemical treatment, has an acidity less than 2%, and is judged to have a good taste. Over 50% of the oil produced in the Mediterranean area is of such poor quality that it must be refined to produce an edible product. After these two grades come the blends of oil that are primarily refined oil and virgin Olive oil.
Pure olive oil. Oils labeled as Pure olive oil or Olive oil are usually a blend of refined and virgin production oil. Remember, over 50% of the oil produced in the Mediterranean area is of such poor quality that it must be refined to produce an edible product. No solvents used to extract the oil but it has been refined with the use of charcoal and other chemical and physical filters
Olive oil is a blend of virgin and refined production oil, of no more than 1.5% acidity, and lacks a strong flavor.
Olive-pomace oil is refined pomace olive production oil possibly blended with some virgin production oil. It is fit for consumption, but may not be described simply as olive oil. Olive-pomace oil is rarely sold at retail; it is often used for certain kinds of cooking in restaurants.
Refined olive oil is the olive oil obtained from virgin olive oils by refining methods which do not lead to alterations in the initial glyceridic structure. It has a free acidity, expressed as oleic acid, of not more than 0.3 grams per 100 grams (0.3%) and its other characteristics correspond to those fixed for this category in this standard. This is obtained by refining virgin olive oils which have a high acidity level and/or organoleptic defects which are eliminated after refining. Just like Pure Olive Oil and Virgin Olive Oil, over 50% of the oil produced in the Mediterranean must be refined to produce an edible product. Although no solvents have been used to extract the oil, it has been refined with the use of charcoal and other chemical and physical filters. An obsolete equivalent is "pure olive oil"
Pomace olive oil is extracted from the pomace using chemical solvents, mostly hexane, and by heat. Sometimes blended with some virgin production oil. It is fit for consumption, but may not be described simply as olive oil. Olive-pomace oil is rarely sold at retail; it is often used for certain kinds of cooking in restaurants.
Lampante oil is not suitable as food because it is made usually from olives that are spoiled or insect infested.; the term lampante comes from olive oil's long-standing use in oil-burning lamps. Lampante oil is mostly used in the industrial market. It must be chemically refined before it can be consumed. The resulting oil, after refining, is known as A-Refined, or Refined-A olive oil. It is not, strictly speaking, "olive oil." It is used as the primary ingredient for a new product that is sold as "Pure Olive Oil.”. As the United States is not a member, the IOOC retail grades have no legal meaning in that country; terms such as "extra virgin" may be used without legal restrictions. Since 1948 the U.S. Department of Agriculture (USDA)has listed four grades of olive oil based on acidity, absence of defects, odor and flavor: 
U.S. Grade A or U.S. Fancy possesses a free fatty acid content of not more than 1.4% and is "free from defects";
U.S. Grade B or U.S. Choice possesses a free fatty acid content of not more than 2.5% and is "reasonably free from defects";
U.S. Grade C or U.S. Standard possesses a free fatty acid content of not more than 3.0% and is "fairly free from defects";
U.S. Grade D or U.S. Substandard possesses a free fatty acid content greater than 3.0% and "fails to meet the requirements of U.S. Grade C".
With these diverse labeling styles and the small amount of information they provide, the best indicator of a good olive oil is obtained by tasting while keeping in mind the freshness and beneficial nutritional and antioxidant levels.