From Guild of Archivists

Explorer is the term given to those who journeyed to D'ni when the DRC opened it to the public during the First Restoration. Many of these explorers also took on Yeesha's Journey.

During the time that Uru Live was a subscription-based game, players with active subscriptions were given the status of Explorer, as opposed to those who had not yet subscribed. Non-subscribed players were known as visitors. Explorers had access to more content, such as extra Ages and avatar options.

When Uru became free all players became known as Explorers as the subscription service was removed.