Extra virgin is the highest grade of olive oil. It needs to be unrefined, made only with olives and nothing else.
Producers need to take great care to produce extra virgin olive oil. The fruit must be in excellent condition and best pratices must be followed during harvest and processing processes.
To know for sure if olive oil is extra virgin or not, it needs to pass certain chemical testing and a taste test by trained professionals.
The NYIOOC World Olive Oil Competition has developed a web application to make it easy to search for brands to see if they are really extra virgin, as verified by an independent taste panel during the current production year.