Extra virgin is the highest quality and most expensive olive oil classification. It should have no defects and a flavor of fresh olives. It is the only cooking oil that is made without the use of chemicals and industrial refining.
It is made by simply crushing olives and extracting the juice. It must be produced entirely by mechanical means without the use of any solvents, and under temperatures that will not degrade the oil.
It's not easy to produce extra virgin olive oil. A producer must use fresh olives in good condition and monitor every step of the process with great care. Extra virgin olive oil doesn't stay that way: Even in perfect storage conditions, the oil will degrade over time, so it's important to enjoy it within its two-year shelf life.
Source: Olive Oil Times