Probably something to do with the fact that it is mechanically cold-pressed from olives with no chemical intervention, therefore it's unsullied (just like a virgin). Also, it must be very low in free acid, which can't happen if any chemical processes are used to extract it. The "extra" is added because there's a lower grade of olive oil called just "virgin." You may prefer virgins because they're pure and all that stuff, or you may prefer persons of experience who could show you a better time. But with olive oil, avoid all except extra virgin!