What is the differenc between

Besides tasting better there are a number of things. Below is the link to wikipedia

http://en.wikipedia.org/wiki/Olive_oil

Extra Virgin Olive Oil. "Extra" is the highest grade for olive oil--the best you can buy. The virgin oil produced from the mechanical pressing described above may be called "extra" if it has less than 1% free oleic acid, and if it exhibits superior taste, color and aroma. Thus, the "extra" in extra virgin olive oil means "premium," or simply, "the best."

Olive Oil. Ordinary "olive oil" is actually a blended oil product. Olive oil producers start with low quality virgin olive oils. For these oils to be fit for consumption, they must be refined using mechanical, thermal and/or chemical processes. The resulting "refined olive oil" is largely colorless and tasteless. Before the resulting product is sold as "olive oil," the producer blends into the refined olive oil a percentage of quality virgin olive oil to provide color and taste.

"Light" or "Mild" Olive Oil. Light olive oil is a variation on ordinary olive oil. Producers of this product use a highly refined olive oil, and add less quality virgin oil than that typically used to blend olive oil. The only thing "light" about light olive oil is the taste and color; it has the same caloric and fat content as other oils.

Olive-Pomace Oil. Olive-pomace oil is the residue oil that is extracted by chemical solvents from previously pressed olive mash. This oil must be highly-refined to remove chemical impurities. Like ordinary olive oil, refined olive-pomace oil is enriched with virgin olive oil prior to sale.

Olive Oil Blends. Olive oil blends (e.g., canola oil enriched with some virgin olive oil) are sometimes used as a more economical substitute for olive oil (but not as a substitute for extra virgin olive oil). Because the production of good olive oil is labor intensive--the olives must essentially be picked by hand--the resulting product is more expensive than other vegetable oils. To offer a more economical product with some of the goodness of olive oil, some companies make olive oil blends. In an olive oil blend, the producer uses a base of a less expensive vegetable oil (e.g. canola oil) to which it adds a percentage (e.g. 25%) of virgin olive oil. These products have proven particularly attractive to restaurant and institutional purchasers where the small savings per tablespoon results in big savings due to the large volume they purchase.