What do "virgin" and "extra virgin" mean in regards to olive oil?

In the US, "extra virgin" isn't a legally protected term - some of the stuff sold as EVOO here would never, ever pass as it elsewhere.

From Wikipedia:

• 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. It is used on salads, added at the table to soups and stews and for dipping.
• Virgin olive oil comes from virgin oil production only, has an acidity less than 2%, and is judged to have a good taste.
• Pure olive oil. Oils labeled as Pure olive oil or Olive oil are usually a blend of refined and virgin production oil.

Cooking-wise, the extra virgin stuff is best used in situations where it won't be highly heated. Salad dressings, dipping oils, finishing a dish, etc. are where it shines.

There are typicality four types of olive oil available, with Extra Virgin being at the top of the quality tree:

Extra virgin olive oil is mechanically pressed (you may see the term cold pressed) rather than being produced by chemical means. I has an acidity level of less than 0.8%. It is also tasted for flavour before being certified.

Fine or Virgin Olive Oil has an acidity of less than 2%. It often uses slighter riper olives. Olive oils with the low acidity of extra virgin but which haven’t passed the official taste test also fall into this category.

Ordinary Olive Oil is usually used to produce refined oils with a bland flavour.

Pomace Oil is processed from the paste left after the first pressing. It is generally quite flavourless and of low quality, usually only used for deep frying.

Exceptional quality Extra Virgin olive oil is still made on hand presses and hence the cost can be quite high.

The International Olive Council (IOC) and the United States Department of Agriculture (USDA) have standards for what constitutes "Extra Virgin" olive oil. It's based mostly on measurable chemical properties, but also some more subjective "sensory" criteria.

If you really want to geek out and know the details, there is a recent study by the UC Davis Olive Center that you should read. They tested major North American brands of Extra Virgin olive oil to see whether they meet the criteria to carry the designation. The results were quite poor.

The paper goes into quite a lot of detail about the specific criteria. Get the PDF at http://www.olivecenter.ucdavis.edu/news-events/news/files/olive%20oil%20final%20071410%20.pdf.

Olive oil is defined by free fatty acid content. Less than 0.8% acid makes it extra virgin, less than 2% is virgin, 2% to 3% acid content is "pure". Cold pressing is antiquated, slow and messy (i have been involved) Continuous processing with centrifuges is quicker, cleaner and at the same temperature. Look for oil which shows the acid content.

In general, "virgin olive oil" is olive juice that had been mechanically extracted from raw milled olives. To be "extra-virgin" the juice should be from high quality fruit that is handled quickly and carefully at low temperatures.

Unfortunately the terms, "extra virgin olive oil" and "virgin olive oil" usually have very little meaning. The quality of an olive oil is very subjective and a lack of useful quantifiable attributes makes regulation almost impossible.

The flavor and cooking properties of olive oil are factors of the fruit quality and the processing methods.

Depends. Extra virgin could mean first press of the olive. Of good quality. A light pressing. To mash the olives. Next the pits are removed. Then a repress of the meat for oil. Virgin oil. Next the pits are pressed. for dark oil. Next all is thrown together & repressed for the dregs. But today it is done different It has to do with acid content & color, smell. Centrifuges are used today.